Hi folks,
We're in discussions with a builder and an architect about reinforcing the existing floor joists in our attic in prep for an attic renovation. The house was built in the early '30s. The existing joists are "true" 2x6s and I think are roughly 16" OC (I say "roughly" because there seem to be a lot of exceptions to the rule, leaning toward the "more crowded" side). The span is roughly 11 or 12 feet or so on each side.
Our conundrum is that, even though we are considering adding a dormer, we want to retain as much head room as possible. We have a few of those "Attics and Basements" type books from Home Depot etc. They typically say to sister with the same lumber as the original.
However, the architect consulted with an engineer (who has not seen the house) and apparently the recommendation was to sister with 2x10s! Adding a new finished floor to this means we would be losing another 5 inches or so of head room. The existing roof is a typical "triangle" shape (not an expert here!) and I think it is something like 8'2" in the middle, at the top of the center ridge line... so one doesn't have to wander far from the middle before one would hit one's head.
Note that apart from a possible shed dormer, we are not adding another floor or anything. We just figured that 2x10s seem like overkill when these "DIY" books say we can sister with the same lumber.
Also, if we "must" sister with something beefier, what about using engineered lumber somehow? It seems that an "I-beam" or "LVL" board of less than 10" height would provide the "same" strength without the loss of headroom. However, I have been unable to find anything on the web that explains how one would actually sister a "conventional" 2x6 with an I-beam or LVL, or whether this is even doable and/or recommended in the first place. Isn't LVL a lot heavier than conventional lumber? Another idea that I've heard was that it seems it might be possible to just interleave new I-beams (higher than 6") between the existing joists, effectively neutralizing the old boards, save for their own weight still being in the picture.
Obviously what seemed to start out as a straightforward concern has ballooned into a confusing web of questions! Any suggestions/ideas would be much appreciated.
Thanks
We're in discussions with a builder and an architect about reinforcing the existing floor joists in our attic in prep for an attic renovation. The house was built in the early '30s. The existing joists are "true" 2x6s and I think are roughly 16" OC (I say "roughly" because there seem to be a lot of exceptions to the rule, leaning toward the "more crowded" side). The span is roughly 11 or 12 feet or so on each side.
Our conundrum is that, even though we are considering adding a dormer, we want to retain as much head room as possible. We have a few of those "Attics and Basements" type books from Home Depot etc. They typically say to sister with the same lumber as the original.
However, the architect consulted with an engineer (who has not seen the house) and apparently the recommendation was to sister with 2x10s! Adding a new finished floor to this means we would be losing another 5 inches or so of head room. The existing roof is a typical "triangle" shape (not an expert here!) and I think it is something like 8'2" in the middle, at the top of the center ridge line... so one doesn't have to wander far from the middle before one would hit one's head.
Note that apart from a possible shed dormer, we are not adding another floor or anything. We just figured that 2x10s seem like overkill when these "DIY" books say we can sister with the same lumber.
Also, if we "must" sister with something beefier, what about using engineered lumber somehow? It seems that an "I-beam" or "LVL" board of less than 10" height would provide the "same" strength without the loss of headroom. However, I have been unable to find anything on the web that explains how one would actually sister a "conventional" 2x6 with an I-beam or LVL, or whether this is even doable and/or recommended in the first place. Isn't LVL a lot heavier than conventional lumber? Another idea that I've heard was that it seems it might be possible to just interleave new I-beams (higher than 6") between the existing joists, effectively neutralizing the old boards, save for their own weight still being in the picture.
Obviously what seemed to start out as a straightforward concern has ballooned into a confusing web of questions! Any suggestions/ideas would be much appreciated.
Thanks