Please help me with my deck that is being built right now
June 9, 2020 7:28 PM   Subscribe

Our deck is being replaced this week after we found serious structural issues. We had to get it done as soon as possible, so we chose a contractor we used once before for a small project, who was recommended by friends, whose work we've seen. Today the deck boards began to be installed and they have A LOT of knots. The deck boards are SPIB stamped standard grade (SPIB STAND R.E.D. KD19 HT 341). There is no issue with the work, everything looks very well done. I'm just surprised and concerned about the deck boards. If you're a contractor, or someone experienced in these matters - is this an acceptable grade of deck boards? Are the knots going to cause any problems with the wood rotting or with maintaining the deck? (Should I ask them to rip it up and use a better grade of wood?!) We're outside of Charlotte NC in the US, in case that matters. Thanks MetaFilter!
posted by racersix6 to Home & Garden (9 answers total) 1 user marked this as a favorite
Can you be more specific about the number of knots? How many per square foot, and can you see through the board?
posted by bbqturtle at 7:37 PM on June 9, 2020

Are the knots actual holes causing an opening clear through the board? Or just cosmetic? Carpenters look for other defects in wood like bowing, twisting, cupping, checks and splits, which are generally more important than cosmetic knots as some of those can prevent production of a square and level surface.

See if you can edit your post with photos - it would be helpful to be able to see what you are talking about.
posted by zdravo at 7:46 PM on June 9, 2020 [1 favorite]

Any which way, make sure they're installing the boards so the center of the tree is below deck. This significantly reduces cupping as the wood ages.
posted by notsnot at 7:47 PM on June 9, 2020 [2 favorites]

Thank you - while I try to figure out how to add photos: you cannot see through the knots, there are no holes. But some of them are very dark and look like they could be popped right out of the wood.
posted by racersix6 at 7:49 PM on June 9, 2020

See if you can pop one out. If you can, bring it to the attention of the contractor and have a discussion about the quality of the boards. If you can't pop it out, that is a good thing.

I had knots in the wood of my original deck. We stained the deck and they were not so noticeable. 20 years later when we replaced the deck we went with fake wood. I forget the name of the product, but it was great. No warping, no problem of any kind. I sold the house, but I assume it is still good.
posted by AugustWest at 10:25 PM on June 9, 2020 [1 favorite]

some of them are very dark and look like they could be popped right out of the wood.

Even if they can’t actually be popped out, a dark, possibly gappy, ring around the knot means it’s a “loose knot” and is something that causes boards to be downgraded. They’re not a structural problem unless they’re very big, but knots will degrade faster than surrounding wood. There’s a big range of acceptability here, depending on how finicky you are, and how much you’re willing to pay for better material.

Here’s a SPIB grader’s reference sheet for radius-edged decking.

Note that SPIB “premium” limits both the size of knots and the sum of their average diameters over any 4’ length, whereas standard grade permits knots that are 50-67% larger with no limit on their number as long as they aren’t clustered very close together. “Standard” is simply cheaper, lower-quality material, but that doesn’t mean it’s unacceptable. Does your contract stipulate a particular grade? Are you willing to pay more?
posted by jon1270 at 4:14 AM on June 10, 2020 [2 favorites]

Well it's finally my time to shine. I was an actual bonafide and certified SPF* lumber inspector at several stud grad mills back in my youth.

Short answer: knots are mostly fine. Southern Pine is the second strongest type of common lumber, standard lumber is fine, your deck is not being assembled out of the the cheapest options.

Some folks like how knots look, some don't. People who use hand tools generally struggle with them, large ones can cause weakness. There is a formula for the total number of knots over a certain distance - I looked it up and for this grade it's 'the sum of the knots in 6 inches can't exceed an area twice the size of the max allowed knot." For a six inch board that is 5 inches for a 4 inch board that's 3 inches.

The stamp SPIB STAND R.E.D. KD19 HT 341 is
  • SPIB :Southern Pine Inspection Bureau: SPIB is the big standardization body for this type of lumber
  • STAND: standard board: as Jon1270 linked - well knotted. Not the best, but not the cheapest
  • KD19: Kiln Dried to 19% humidity. Fine for outdoor use and again, not the cheapest
  • HT: Heat Treated - this is to kill pests in the wood and means it might be imported wood
  • 341: The plant # the board was finished at
  • R.E.D. Radius Edge Decking - that just refers to the shape of rounding (its edge has a radius)
The difference between a deck made out of premium materials and yours is mostly aesthetics and your deck will be practically as strong as one that would cost considerably more.

*the weakest of commonly available timber
posted by zenon at 9:32 AM on June 10, 2020 [31 favorites]

What does your contract specify? You do have a contract with a scope of work, right? It should specify the grade of materials.
posted by summerstorm at 10:05 AM on June 10, 2020

Thank you, everyone! This was great information and made me feel comfortable with keeping this grade of wood. We had the contractor replace some of the deck boards, so all is well.
posted by racersix6 at 3:42 PM on June 11, 2020

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