What do we need to know before we build our house?
December 1, 2013 3:36 PM   Subscribe

We are preparing to build a house. We've been doing this for many months, have talked to architects, contractors, and our city's planning and building department, and we still have lots of questions. Lend us some expertise on foundations, design, and construction?

The house will be less than 500sqft, will probably be 2-story, and will be located in Portland, Oregon. We have no prior construction experience, are drawing the rough plans ourselves but will employ an architect to finalize the drawings. We will act as owner-builders, hire a contractor to build the shell (foundation, framing, floors, roof), and finish the work ourselves with help from friends and other contractors.

We want to favor sustainable building practices, primarily using natural and reclaimed materials. Our starting budget is $40k, and we're reserving a buffer because everyone assures us that it will cost twice as much as we expect.

1) What kind of foundation do we need? Concerns include wet, clay-ey soil; earthquakes, weight. Would pier-and-post be sufficient? Why don't we see more pier-and-post foundations around? Slab with hydronic heat seems to be all the rage these days but I have yet to be convinced. Bonus challenge: If we want a masonry heater (specifically, an 1870lb+ rocket mass heater), what would be necessary to support it?

2) I understand we're supposed to design simple boxes sized in 4 foot increments to keep cost down, because lumber, plywood, etc. is made in 4 and 8 foot increments. How terrible is it to break this rule? Are we looking at a substantial cost increase (beyond the standard $50-$100 per square foot) if we go from a 12x16 to a 12x18 footprint?

3) What sort of insurance do we need as owner-builders, and what can we expect it to cost?

4) What resources would you recommend? We've read several construction and design books and we're getting very familiar with city and state code. What else?

5) What other questions should we be asking? What do you wish you had known before building your own house?

posted by sibilatorix to Home & Garden (14 answers total) 15 users marked this as a favorite
There's this company callled Tumbleweed that specializes in selling plans for small homes, and they also do workshops and books and stuff for learning about the basics of building your own house. That might be a place to start.
posted by bleep at 4:22 PM on December 1, 2013

You'll almost certainly need a geotechnical engineer to do soil tests to determine load-bearing capacity, for the foundation. Clay soils have a number of bad characteristics (swelling and shrinking) that make it problematic for foundations. For example, a few years of drought can dry out your soil differentially, and your concrete perimeter foundation can fail when portions of it become unsupported.

You are probably not competent to design the foundation for your one ton masonry heater, and might require a geotechnical engineer to design that and your spread footing foundation. While a ton is not that much to ask of two or 4 square feet on a reasonable substrate, you probably won't be able to get your plans through the county without some engineers stamp on them.

You'll almost certainly need a structural engineer, to verify or design seismic safety. You need to tie your house to foundations with approved brackets. You'll need shear walls of particular sizes and strengths, and you might have to change the design of your house to accommodate them.

You may require an NFPA-13D residential fire sprinkler protection system, and you cannot design one of those yourself (unless you are in an enlightened area that allows you to use the prescriptive approach outlined in that excellent document). From my own experience, the county fire-marshal was the most obstructive and most frivolously useless lump of flesh that I had to deal with. When I finished installing my fire sprinkler system, I was informed during inspection that the plans that had been approved by the fire marshal's office could not be signed off, as my shutoff valves were non-conforming.

If you do install your own NFPA-13D compliant system, remember that if an area is accessible with anything other than a door just big enough to slide a water heater through, it is possible that you will have to install sprinklers in it: hence, my CRAWL SPACE that has a fire sprinkler system in it (walk-in basement that tapers down to a crawlspace). Also, if you are installing fire sprinkler pipes that are "protected" (that is, behind drywall), you can use the slip-fitting PVC pipe designated for that purpose. If it is "unprotected" (in crawlspaces or the garage) you will have to use black iron or galvanized pipe. You would very much rather use the slip fitting glued PVC pipe: the pressure test for fire sprinker systems is severe, and getting pipe threads that don't leak under 100PSI plus is a challenge (hint: for every inch of pipe diameter, you need one foot of pipe wrench. 4 inch pipe, 4 foot wrench).

You might not be allowed to do your own fuel-gas plumbing in your state, and may have to contract someone else to do it.

We installed hydronic radiant heat in the subfloor and basement slab: If I was doing it again I would go for hydronic radiant heat in baseboard heaters.

Pay someone to pour and finish any slabs you create. You can put in the forms, and the rebar, but let someone else do the pouring and finishing. Don't ever accept a hot load of concrete: send it back.


It'll take longer to get your plans through the regulating agency than you think. Some of their demands are unreasonable, and should be challenged. Some of them are unreasonable, and should not be challenged. Good luck.
posted by the Real Dan at 4:23 PM on December 1, 2013 [8 favorites]

My initial response is a resounding, "RUN! WHILE YOU STILL CAN, RUN!" but that's probably not entirely helpful. My credentials in answering are that as a girl, I helped my parents build their own house--I swing a mean hammer! The spousal unit also has helped build various edifices, not for a living. We purchased a 1916 Arts & Crafts style bungalow in need of a great deal of work. We've worked hard on this place for about a decade now, investing sweat equity and paying professionals only for what we cannot do--HVAC, electric. We've replaced the whole danged roof, including (rotting) rafters and decking. I've climbed up scaffolding and repaired, painted and stained trim and stucco. We're both very DIY, skilled and talented, had read all sorts of books and were game to try anything. So I am very familiar with the lure of DIY--it's my default mode.

That being said, I will also recommend hiring two professionals: First, invest in an architect who specializes in sustainable/green residential design. As you are discovering, there are a lot of interconnected systems in a house, and that's what architects are trained to wrangle into line. Second, if you haven't already hire a general contractor. All those interconnected systems in a house are dealt with by various and sundry subcontractors (or you, if you have the ability) and it is the general contractor's job to wrangle all those into line. If you hire these two people, you'll be in good shape.

Now for a couple questions:

1. Have you had a site review? "Wet, clay-ey soil" can be problematic for building. How problematic? Only an expert can tell you.

2. How old are you? How good of physical shape are you in? Construction is hard, heavy work, and if you've never done any, it will be doubly hard because you will not have muscle memory for the actions--everything will be new and HARD.

3. Are some of your "other contractors" plumbers and electricians? You do not want to install those systems yourself with no training and it's probably illegal. Also, make sure all your contractors pull the appropriate permits. That's one of the issues a general contractor will deal with, which is another reason to hire one.

Good luck to you! Happy house-building! Enjoy the challenge! Also, try your best to stir some pragmatism into your DIY dreams. There's no shame in letting professionals do what they've trained for years to do; you'll be happy you did.
posted by miss patrish at 4:39 PM on December 1, 2013 [4 favorites]

The 50-100 bucks a square foot number is likely to low. The conventional number for minimum code housing is 80 a square foot builders cost for the house in large conventional subdivision on a small (5500-6000 sf lot), and small house design and sustainable/green design add to this number. I wouldn't be surprised if the final number is closer to double that, or 150-200 a square foot. If you do a LOT of the work yourself you can keep it down, but I don't think you can do it for less than 100 no matter how hard you try.

A big problem with small house design is that the really expensive stuff like foundations, furnaces, kitchens and bathrooms are a much higher percentage of the house square footage and don't get averaged in over large cheap rooms like the dining rooms, living rooms and bedrooms. The exterior walls are also a much higher percentage of the overall cost as well and super insulated walls and triple paned windows aren't cheap. This is why you don't see much built new at less than about 1300 square feet-that is about the break even point where more square footage actually costs you more money. You can make back some money on smaller furnaces and such, but there are code requirements to be meant and to get around them you have to have an engineer design them and stamp them which isn't cheap and sometimes this cost is more than just buying the larger, more conventional system.

And yeah, you need a geotech engineer if you aren't going with a conventional foundation. Post and beam is just fine on suitable soils. Spread footings/slab on grade is great too and actually better in an earthquake if the concrete is reinforced. It is also possible to insulate the foundation on a slab and get some real gains that way.

Hydronic/radiate floor heat is great. It is a more compact, efficient system and very well suited to small spaces. You don't have to have chases for the forced air, it is a gentle even heat that feels better and you can use a variety of different heat sources (heat pump/gas/oil/solar hot water (not going to work well in Portland in the winter).
posted by bartonlong at 4:52 PM on December 1, 2013 [3 favorites]

You are going to chew up around 15-20% of your less than 500 square feet with your stair case. Unless you are just talking about a ladder accessible loft I'd strongly recommend keeping such a small house without a basement to a single story. It might even be cheaper. Also a two story house with a 250 square foot foot print is going to look weirdly tall; more like a tower than a house.

sibilatorix: "Are we looking at a substantial cost increase (beyond the standard $50-$100 per square foot) if we go from a 12x16 to a 12x18 footprint?"

For such a small house and using a half module (IE 2' instead of 4') it's not going to make much difference at all; maybe 20% more for the 15% more space. This is more of an issue if you wanted a 13 x 17 house or had a bunch of deviations from a rectangular box. In addition to what bartonlong said about break even sizes a corner costs easily twice as much to build as a flat wall and you are going to have a lot of corner relative to the amount of wall you have which is going to raise your price per linear foot of wall.

And yes hydronic is great for small spaces (well it is great generally but especially for small spaces). A tiny little demand hot water tank can provide both domestic hot water and heat without taking much in the way of floor space at all.
posted by Mitheral at 5:40 PM on December 1, 2013

1) If you have substandard soils (i.e. clay) and are in a seismic zone, you may need to hire somebody to figure out your foundation. Alternatively, there are code standards for minimum bearing weight without doing soils testing or structural engineering, and your local building department likely has prescriptive building standards for homeowners doing the kind of thing you'd like to do. All that stuff goes out the window if the inspector finds expansive or liquefiable soils (i.e. organic material, certain types of clay, uncompacted fill, etc.) in your building site or you're on a fault line. Going for two stories instead of one may also preclude meeting those requirements. Pier and post foundations still exist, but there's usually a perimeter foundation wall around the structure. In seismic zones, there may be interior foundation walls to provide shear resistance. There are a couple determining factors for whether you go with a raised floor (pier/post foundation) or slab, and structural concerns are generally minor because you can always design them to be however strong they need to be. The main factors are cost, adaptability, and weather. If you live in an area where there are standards for how far your foundations need to go below grade because of the frost line, you may want some kind of crawlspace under your house. If you have any thought about underbuilding certain utilities right now and adding more stuff later (like, more bathrooms or something, possibly telecom or electrical wiring), you'll want a crawlspace. If you just want it to be cheap, you'll want a slab.

No one on an internet question and answer site will be able to specifically design your foundation for you.

2) The 4' module standard is just because of the labor cost of cutting materials and the material cost of throwing away scraps. One way or the other, you're going to break it, whether you like it or not. If your framed wall measures 16' exactly on the outside, hooray, it takes exactly 2 plywood sheets to cover the length; but your interior is going to be something like 15'-1", and drywall also comes in 4'x8' sheets (you'd generally want to favor cutting drywall over cutting plywood since it's cheaper). And then you have windows and doors. Are you putting in a 4' door? Are all your windows 4' wide? Just worry about having 4' of continuous solid wall on every length of exterior wall face and don't sweat anything else - you're going to be cutting up plywood and gyp all over the place. With a house your size out of wood framing, I don't think you'll be saving much.

You may want to take your sketches down to the building department and see if they have some kind of early-assistance over the counter help you can get on looking at potential issues with your home. They may be able to point out potential problem areas that you won't be able to handle yourself.
posted by LionIndex at 5:50 PM on December 1, 2013

Two-story: Are you absolutely set on two-stories? The problem is that in a 12'x18' footprint house, you will lose roughly 20% of your gross square footage to stairs and landing, assuming you go with the bare minimum. Assuming you want to build something energy-efficient, you need reasonably thick insulation - that means walls that take up another 15-25% of your building footprint. One story makes much more sense if you can make it work in any way.

Cost: Per square foot costs are not that useful when you are building very small. You will pay significantly more per square foot. Think about all the mechanical and electrical systems that don't really scale (you still need electrical service, some sort of heat system, ventilation, appliances, a kitchen, etc.). I don't think $40K is even close to reasonable.

Foundation: I think slab probably makes the most sense in your climate (well insulated underneath, of course). If you want storage space, a full basement that is carefully thermally isolated from the rest of the house (separate entrance) can make sense. You would want something more substantial than pier and post for a masonry heater. Other than saving some concrete, I don't see the advantage of pier and post over slab on grade.

Radiant heat: It certainly is nice, but it isn't cheap to install and if you have a well insulated house, you don't need it.

Masonry heater: In your climate, in a very small, and presumably well insulated house, a masonry heater will be overkill. I suspect you would overheat with any fire that is big enough to start to burn cleanly. Build a well insulated shell and you will find that the heat from your appliances, electronics, human bodies, etc. will keep the temperature up quite a bit. Use a small air-source heat pump (minisplit) or just plain electric heat to make up the rest. Do the heating load calculations before building to bear this out.

Ventilation and air sealing: There are a lot of great resources out about building a well sealed house for energy efficiency. This is one thing you want to do right the first time as it is much harder to retrofit. Make sure you provide sufficient ventilation.

4-foot multiples: This cost is going to be very minor in the context of such a small house. Maybe hundreds of extra dollars.

Resources, Green Building: Using reclaimed and natural materials is great. Bear in mind that the embodied energy in a house is quite a small proportion of the total energy used by a house over its lifespan (for regular construction, somewhere around 10%). So if your concern is environmental sustainability, favor energy efficiency over re-using or using natural materials. There are lots of great passivhaus resources out there and lots of good green building resources (greenbuildingadvisor.com is pretty good).
posted by ssg at 5:55 PM on December 1, 2013 [1 favorite]

You're really talking about building a 12x16 house? Really? And you think you can do this for $40k?

Well, for one thing, I'd be pretty surprised if you could actually get the municipality to approve something like that. That's not a house. That's not even a cabin. My one-room efficiency apartment in Harlem was almost 400 square feet. Hell, my in-laws tool shed is at least 12 x 12. And you're trying to build a free-standing single-family home that size? I mean, I get the fact that McMansions are a waste of space, resources, and energy, but good gravy, there's such a thing as taking it too far. I would not be at all surprised if the zoning board takes issue with your proposal.

On to your actual questions.

(1) Impossible to say. You'll need to pay an expert to come out to do soil analysis. People think that the ground is permanent and that you can basically build anything anywhere. Nothing could be further from the truth. Soil types vary widely, and the impact of grade cannot be overstated. What kind of foundation you'll need will depend entirely upon the condition of the property.

(2) I think you'll find that the $50-100/sq. ft. rule of thumb only really applies to houses in excess of 1,000 square feet. Three main reasons.

First, whether you're building a 500 square foot house or a 5,000 square foot house, there are certain things which have to go in both, and which you'll only need one of. You'll need an HVAC system, and whatever your main unit is going to be, it's going to cost most of whatever unit would be going into a much larger house. By comparison, the vents and registers are rounding errors. Same goes for things like a breaker box, a dishwasher, a bathroom (2BA cost more than 1BA, but 1BA still costs 1BA), etc. There are just certain things which every house needs, no matter how large, and there's a minimum cost there.

Second, have you ever heard of the square-cube law? Simply put, as you increase the size of a solid, the volume increases faster than the surface area. A 2-foot cube has a surface area of 24ft^2 but a volume of 8ft^3. A 6-foot cube has a surface area of 216ft^2 and a volume of 216ft^3. And a 10-foot cube has a surface area of 600ft^2 and a volume of 1000ft^3. Etc. Most of the cost in a house is in the surfaces: floors, roofs, and walls. Thus, as houses get larger, the ratio of cost to cubic foot of living space goes way down. The converse of this is that as houses get smaller, they get more expensive, relatively speaking.

Third, it turns out that there are fixed costs to labor too. Think about painting a room. You've got to get the paint together, set up your ladders, paint trays, rollers, etc. And when you're done you've got to tear all of that down and clean it up. This will take precisely the same amount of time whether you're painting a 10 x 10 bedroom or a 20 x 30 finished basement. Granted, the larger room will take longer to do, but the smaller your room gets, setup and tear down will take up a larger and larger percentage of the overall time. And that's going to apply to basically everything you do. Hanging an extra ten sheets of drywall may take an extra ten minutes, but basically any drywall job is going to take half a day, minimum, so hanging those extra ten sheets costs almost nothing, marginally speaking.

In short: a 5,000 square foot house is almost always going to cost more than a 500 square foot house, but it not ten times as much. Maybe only two or three times as much. And a lot of that cost may well be tied up in the lot. I think you'd be surprised how little some of these McMansions cost to build. I'm not saying that you have to build one, but if you're assuming that the cost of building a house bears a linear relationship to the square footage, you're just wrong. And I think that you may find that going from a sub-500 square foot house to a 1,000+ square foot house may not actually cost you anything, or at least will cost you drastically less than you probably think.

(3) Well you'll definitely need a builders' risk policy, but that'll just cover the building and materials while the house is being built. I don't think you'll be able to buy insurance for faulty workmanship. If you were to hire a contractor to build it for you, they'd have that insurance, but you're not going to be able to buy insurance for your own negligence.

(4) Hiring a professional. There's a reason people make a living building houses. It's because building houses is hard. You are not well-positioned to do this for anything like a reasonable cost.

(5) Have you really thought this thing through? Do you realize that it will cost radically more to fix this thing if you screw it up than it would to just pay someone to get it right the first time? Do you realize that a lot of the work you're doing requires professional licenses, and that the code inspector won't necessarily even want to come out if it hasn't been done by a licensed professional?

*Which is one of the reasons there's been a trend towards McMansions. The bigger the house, the smaller percentage of your total labor you spend on that minimum, increasing your productivity.
posted by valkyryn at 6:00 PM on December 1, 2013 [1 favorite]

Response by poster: There are a few basic points I forgot to mention:

- We aren't building small in a misguided effort to save tons of money - we knew the $50-100/sqft estimate was off, but hadn't run across alternative figures for smaller construction. (Thanks bartonlong!) Our lot is 3000sqft, and because it's a flag lot the buildable area is just over 1000sqft. We want some yard left when this thing is done. This is also why we're favoring 2-story with a smaller footprint.

- We've considered everything from 12x12 to 16x20, single and double story. Drew lots of designs with lofts/ladders/etc. We'd prefer the 2-story so we can have a second space separate from the downstairs kitchen/living area, and stairs are required for it to be permitted as anything more than an attic.

- In talking with the city and reading code we've sorted out a lot of the details. They've assured us that the size is fine so long as we have basic necessities as specified by code.

- We will be hiring an experienced contractor for the shell, and to advise us on the work we do ourselves. We'll hire licensed, experienced professionals for plumbing and electrical.

- The masonry heater sounded like an interesting prospect, but from comments it sounds less reasonable now.

Thanks everyone for the advice! LionIndex and mitheral, that really clarifies the 4' module standard. Valkyryn, thanks for mentioning the Builder's Risk policy. Does that also cover issues like a contractor getting injured on-site? ssg, that figure for embodied energy of building materials was helpful to see - I didn't know it was so drastic.

I really appreciate the comparative analyses of foundations - I've been trying to find that info for months with no success. We'll probably be favoring an insulated slab now, in spite of the extra concrete.

Anyway, many thanks! Further advice and more resources continue to be welcome!
posted by sibilatorix at 6:45 PM on December 1, 2013 [1 favorite]

For the stair - your second story will probably be small enough to just use a prefab spiral stair instead of a full-fledged framed one, which may save you quite a bit on how much floor area it takes up.
posted by LionIndex at 6:50 PM on December 1, 2013

Our lot is 3000sqft, and because it's a flag lot the buildable area is just over 1000sqft.

That explains a few things, but I still think the whole project is ill-conceived. What you're looking at here is not a developer making reasonable use of available property but carving up the property into as many lots as technically possible to maximize his profit, even if that means that some are practically unusable. Like yours. Even going to a 750 sq. ft. footprint would drastically improve the viability here.

thanks for mentioning the Builder's Risk policy. Does that also cover issues like a contractor getting injured on-site?

Most contracts between an owner and general contractor require that the general carry workers' compensation insurance and indemnify you for any injuries that happen to him, his employees, or subcontractors. But you'll want to talk to your broker about getting liability insurance for that, because if someone is injured, they're going to sue you anyway. You can probably avoid liability with the right contract, but unless you have insurance, you'll have to pay for a lawyer to assert that defense.
posted by valkyryn at 1:34 AM on December 2, 2013

I'm not sure I agree with the premise that the lot is unusable but I do agree with building the largest home you can afford. It's costly to add on once you discover you've built too small. I'd also as a matter of course get the lot professionally surveyed prior to starting building. Builders IMO have often made mistakes in their subdivisions' lot lines and what is recorded. You will lose space due to stairs, however smart plans can use the space under it effectively or the prefab spiral staircases use the minimal amount. As far as foundations go - what are your neighbors using? What have been their experiences? If I were you I'd add to your plans a shed on the property - lightly insulated (no plumbing or electrical to keep costs down and not provoke the ire of local officials) to make up for the loss of the basement. Will your home have any attic space or crawl space?
posted by lasamana at 5:24 AM on December 2, 2013

I'm going to be as kind as possible here, but you don't know enough to do this. You have been getting EXCELLENT input in this thread but you don't go from 0 to 60 in building a house.

Have you build anything before? That's going to be HUGE!

Look into homes that are built off-site and are assembled on your lot. They fit in with your budget and the process will be SO much easier.

Clayton Homes is one builder.

Stillwater Dwellings is another. The have floor plans for 950, 585 and 400 Sq Ft. The use sustainable building products.

These builders can work with you to cover all of your concerns.

I SERIOUSLY urge you to rethink.
posted by Ruthless Bunny at 5:46 AM on December 2, 2013 [1 favorite]

My house is 20x30, and has plenty of space. I'd go 12X18 or 16 x 18, because resale value is a real thing. I have a spiral stair to the basement and many people can't use it comfortably. The stairs to the tiny 2nd floor are poorly designed, and unpleasant to use. My ceilings are 7' or 7 1/2' feet, which feels cramped. Lots of windows really helps the house feel larger. I can heat the living room and keep the rest of the house above miserable with a small wood stove, but I have to keep adding wood. So, think about ceiling height, and be careful about making it too cramped.

Think about how you will live in the house. Orient windows to things that are nice to look at. My house was converted from a summer cottage, and I so wish it had a saltbox roof, because I have decent solar exposure, but it's not really optimized. My wood stove is the focus of attention 8 months of the year, and it's not in the best location.

There may be a ReStore or other place you can get good windows and doors. Don't go cheap; these are massively important for saving energy and for comfort. Contractors use ReStore and stuff goes fast; be really nice to the staff, maybe they'll call you when something comes in that you're looking for. You'll need a truck or van, and you should be in the habit of looking for opportunities to scavenge. I see so much great stuff in dumpsters - ask for permission, and be super tidy.

I love the floor plans of the Sears houses and you can find plans online. Take plenty of time to plan. Changes get expensive. My son worked with a builder, building the guy's home. The changes were not only expensive, some of them either look weird, or created weird spaces.

During building, be compulsive about sealing crevices and holes and fitting insulation correctly; this will make a big difference in efficiency. Consider having a contractor as a consultant because you have to comply with building codes. A lot of them are for safety and efficiency, so it's a good thing. You should be able to be considered a contractor at Lowe's, Home Depot, etc., and can get a discount. Freecycle and Craigslist/zip (free) are your friends. I got my kitchen from Ikea when they had their sale, and I'm quite happy with it.

In addition to being more expensive than you think, it will be stressful, there will be crises, stuff will break, get stolen, get done incorrectly, etc. Make the time to care for your relationship, or it could be in jeopardy.
posted by theora55 at 9:53 AM on December 2, 2013

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