How best to turn an old MA attic into more functional space?
February 18, 2010 5:58 AM   Subscribe

I'm looking into insulating my attic and turning the area into more than just storage, but am now lost in Google Search Fugue. How do I do it?

Our attic caps the 'new' wing of our house (built in the 1880s as opposed to the 1850s) and is just above our bedroom. It is not insulated. I would like to insulate it and possibly turn the attic into a sort of Nerd Cave where I can paint toy soldiers, store comic books, and maybe even have a chair to read them in.

I figured this would be an easy project - lay some insulation, replace the floorboards, run some new wiring, and we're done. BUT! Googling and flipping through DIY books at the local Home Depot has introduced all sorts of contradictory advice (Seal the attic! No! Vent the attic! Insulation! Vapor barriers! Radiant barriers!) and left me in a state of DIY existential crisis. At this point if someone told me that I had to keep rodents up there to increase the R-factor, I'd believe them.

Here are the details:

- We're in MA.
- The room would 12' long and about 7' wide when the minimum 5' of code-required wall height is taken into consideration. Beyond that there would be about another 3 feet of storage space on each side. (these are rough estimates)
- There is one window.
- The roof has no overhang, so no soffit vents.
- I am 85% sure there is a ridge vent. The roof is only 8 months old.
- The beams and joists and so on are overbuilt according to the 19th century "lets use more lumber" approach.
- We are in a windy area and are usually buffeted by breezes off the North River.
- The attic was too hot to be usable last summer. It has been tolerable, if a bit chilly, this winter.
- We do not have central AC, but do use a window unit in the bedroom below the attic in the summer.
- The previous owner made a half hearted attempt to turn the attic into more usable space, but did not get very far.
- I am fairly handy, having helped to rewire the basement, built shelves and furniture, can hang drywall, and am armed with a pretty good selection of tools.

The goal:

- Reduce heating bills in the winter and make the attic room tolerable in the summer.
- Retain storage capability.
- Not involve a contractor. We've hit our limit for our willingness to deal with contractors this year. We've had roof dudes, siding dudes, multiple plumbing dudes, heating dudes, foundation dudes, tile dudes, and electrical dudes. My pregnant wife is on edge to begin with and I fear dealing with another dude will lead to her standing bloody over a dead body.
- I really don't want it to 'rain' in the attic.
- I don't mind leaving the rafters/roof beams exposed if needed.

So what do I need to do to achieve my goal?
posted by robocop is bleeding to Home & Garden (7 answers total) 4 users marked this as a favorite
Insulating the attic floor won't help for what you want to do. You need to put the insulation between the living space and the weather, which means filling the spaces between rafters with insulation, and covering the insulation with something -- probably drywall.

You will need to add ventilation channels between the insulation and the roof decking, with an entry point for cold air near the bottom, and an exit point for warmed air at the ridge. Since you don't have overhangs you can't do soffit vents, so it's probably easiest to build insulated knee walls, and vent the space behind them to the outdoors. With that, a ridge vent and the channels above the insulation, you've got your ventilation arranged.
posted by jon1270 at 6:22 AM on February 18, 2010 [1 favorite]

If you are going to build a habitable room up there, you don't want to insulate under the floorboards. The reason the space is tolerable in winter is that it's being heated from the room below, and it's probably not very well vented. So you have an either-or choice.

CHOICE A: Insulate the attic floor. Lay down a vapor barrier first (plastic sheeting is fine), then unfaced insulation bats. Or, use foil-faced insulation and lay it down with the foil facing DOWN - toward the heated space. Be sure the attic space is well ventilated - DO NOT SEAL it up. If there is a ridge vent, that's great, but then you also need good-sized rectangular vents in the eaves, at both ends if possible. The space will be hot in summer, cold in winter.

CHOICE B: if you want a usable space up there, you need to insulate the underside of the roof, again with vapor barrier facing the living space. This gets much more complicated and you should buy one of those plan books to show you how it all goes. It will entail knee walls, creating small attic spaces at the sides, which need to have insulation on the floor as above. Those spaces need to be well vented also. As Jon1270 says you'll need vent channels behind the slanting ceilings, and there are all kinds of finishing options. Do buy a plan book. Read up on the why's and wherefore's of venting, that's pretty critical.
posted by beagle at 6:26 AM on February 18, 2010

Home Depot or Barnes and Nobel should have books specifically about finishing basements and attics. As you've discovered though, there is lots of conflicting information out there and even different contractors would do it differently. I've found most books are written for new houses where everything is built to modern code and everything is perfectly square. Very few houses are actually like this. You might want to seek out books and articles written for old houses. I think there's a magazine called "New Old House" or some such that might be helpful.

I'm a bit confused since you seem to have conflicting ideas. If you want to reduce heating bills you'd probably want to insulate the attic floor. If you want to make the space more livable you'd want to insulate the rafters.

To make it usable, I would insulate between the joists. If you insulate the floor you'll just keep heat out in the winter. Normally you would put plastic inserts between the insulating bats and the roof that would create a channel from the soffit vents to the ridge vents. This keeps your roof cooler and helps your shingles last longer. Since you don't have soffit vents this would be pointless. I have wet-blown cellulose insulation in my rafters and the contractor told me with that I don't need the channel. Perhaps he lied, I dunno, but maybe that'll be an option for you.

Personally, I'd insulate the entire roof and then add a knee-wall. If you insulate only to the kneewall and then add cubby doors or drawers, you'll have a lot of un-insulated wall space. You could insulate the kneewall and only have one or two access points with insulation attached to them. If you do this the floor behind the kneewall should be insulated as well.

You generally want a vapor barrier between the living space and the insulation. So you'd want roof --> vent(?) --> insulation --> VB -->drywall/ceiling material.

If your priority is to reduce heating in the rest of the house then forget all that and just insulate the floor. This will probably make the attic much colder in the winter, however, and may not make it much of a nerd cave.

With an insulated roof, I think it'll be tough to make it tolerable in the summer unless you can get some sort of cross breeze. Would it be possible to add another window on the opposite side of the house so you could put in a fan in the summer? You could probably also get some sort of vent/fan to rig up. If you've done wiring that shouldn't be too hard, though cutting a hole in your house can be intimidating. Now that I re-read I see you're talking about a wing, so I guess that may not be possible.

I'm not sure I've told you anything you don't already know, but that's my $.02.

Oh, and congrats to you and B&tP!
posted by bondcliff at 6:40 AM on February 18, 2010 [1 favorite]

Having lived/rented in several New England 3rd floor converted attic spaces, I'd say it's folly to try to make it a crafting/relaxation destination. Even when well done, it will be unbearable to hang out in for at least half the year and disaster for painting models or storing a valued collection. Just wanted to chip in from the "user experience" end since you've already got some insulation experts.
posted by quarterframer at 7:19 AM on February 18, 2010

Nutmegger here. Am just finishing something similar. In short hired someone to spray foam (close cell) into the attic rafters; the rafters are six-inches, so we sprayed to the depth of four inches which is about the best insulation you can get for the R-value. I am putting up the vapor barrier next weekend with some wood and sheet rock to follow.

For the floor, I will be blowing insulation under the flooring mainly for sound proofing as the heating from below would be a positive but I want to drop the noise. I will be blowing the insulation with Ms. fluffy and myself, as you can rent it from Home Depot when you purchase enough of the insulation from them (I believe the last time I did it was 10 bails and the blower is free for the day...but check on that.) This insulation is cellulose I believe. Two people can easily handle the task.

For the attic ceiling, this was done by a contractor. It is nasty stuff with body suits and masks, etc. But in an attic space when you when you want to conserve the working you have, the best insulation you can do is the foam (and you will want to discuss close cell vs. open cell with the contractor.) Once it was done (about 8 weeks ago, the temperature difference was immediate, considering it's winter here. I started working in short sleeves up there again!
posted by fluffycreature at 8:29 AM on February 18, 2010

bondcliff writes "To make it usable, I would insulate between the joists. If you insulate the floor you'll just keep heat out in the winter. Normally you would put plastic inserts between the insulating bats and the roof that would create a channel from the soffit vents to the ridge vents. This keeps your roof cooler and helps your shingles last longer. Since you don't have soffit vents this would be pointless. I have wet-blown cellulose insulation in my rafters and the contractor told me with that I don't need the channel. Perhaps he lied, I dunno, but maybe that'll be an option for you."

There are four reasons to vent the space between the roof deck and the insulation. 1) Reduce deck temperatures which extends the life of the shingles. 2) Reduce temperatures in living spaces under the insulation during the summer. 3) Exhaust moisture that makes it's way through your vapour barrier so that it doesn't rot out your rafters and roof deck. 4) Keep the shingles cold in the winter so that snow blows off instead of melting and forming ice. In Canada completely filling rafter space with insulation is referred to as a hot roof and is only allowed where the risk of blowing snow penetrating your roof vents offsets all the negatives.

If it was me (and I'm speaking to my climate, I don't know how many degree heating days MA gets) this is what I'd do:
  1. Lay down fiberglass batts in the floor space. This isn't for insulation but rather sound attenuation but it will allow you to not heat the attic space in the future if you decide you don't need the space. The floor area which will be outside of your pony walls should be insulated to at least the minimum for your area; around here that would be R40. Cellulose is better/cheap but is a miserable job better handled by a contractor which you want to avoid.
  2. If you don't already have power in the attic then while I was doing that I'd tap into some of the light fixtures for power in the attic space. You're allowed 12 fixtures/outlets per circuit so figure out which are under the max and run some wire from the boxes over to where the pony walls will be. Ideally you'd like at least one outlet every 12 feet (code minimum in Canada) though I'd try to get that down to at least every six feet and the shop I'm building has an outlet every 2' or less.
  3. Lay down your sub floor. Don't fasten the sheets that abut your knee walls as you'll need to move them out of the way when you are installing vapour barrier. If you don't have the ability to get 4X8 sheet material into your attic now is the time to remedy this deficiency if at all possible.
  4. Staple up vent baffles over the heat attic space. These baffles will take in air from the knee wall space and exhaust it out your ridge vent. If you have individual vents instead of a ridge vent then you will need to frame a flat ceiling at the peak far enough below the bottom of your vents so that the ceiling can be insulated to roof standards. this will create a common vent space so that all your rafter bays can vent.
  5. Build your knee walls out of 2x6 material with studs 24" on centre. I'd figure out where 4' head space is and then build the wall 2' farther out from there which would allow you to install built in shelving, drawers, and furniture like desks and seating.
  6. Run all your electrical in the knee wall and roof. Include stuff like cable and phone jacks. Make sure you are installing either vapour barrier flanged boxes or the box wrappers anywhere a box is installed in insulated space.
  7. Insulate wall space and the rafter bays. Ideally your rafter bays will be insulated to your roof R value. You probably won't have enough rafter depth to do this though.
  8. If you didn't have enough rafter space to get your sloped roof up to the minimum roof insulation value apply ridgid insulation to the bottom of the rafters now. The white bead board if fine for this purpose though if you can afford the difference in cost the extruded panels (blue/pink boards) are stronger and easier to work with.
  9. Install a vapour barrier. It's really important that the barrier be continous so take special care to seal every joint with acoustical sealant. This job is going to take forever because you have to run the vapour barrier down in between each of the floor joists and seal it to the vapour barrier at the ceiling below.
  10. Install drywall. Mud, tape, sand and paint.
  11. Install your finish floor.
  12. Pop a beer it's miller time.
Foamed in place insulation is awesome if you can afford it.
posted by Mitheral at 8:38 AM on February 18, 2010 [4 favorites]

Foamed in place insulation is awesome if you can afford it.

you can get DIY kits all over the internet and it's really not that bad, compared to say huffing cellulose dust or crawling through fiberglass, just get yourself a nice tyvek suit, rubber gloves, facemask, etc. but it is expensive.

for slightly cheaper you can just cut regular foam panels to fit between rafters with a small gap and spray foam them tight. that might be a pain but on the other hand i've come to the opinion that, especially with remodelling, it's hard to actually do fiberglass batting insulation right i.e. have a perfect air seal, venting, etc, and there is a big gap between theoretical and actual R-value given that.

also, maybe you should postpone the nerd cave and spend your extra time giving your pregnant wife pedicures, all in all that might be a better investment in your long term happiness.
posted by at 9:34 AM on February 18, 2010 [1 favorite]

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