We are finishing our attic in a 1911 house. The current joists are true 2"x6" with 10'-12' span. We are sistering them with 2"x6" LVLs. We will be adding a bathroom (shower, toilet and sink) and the plumber wasn't sure if drilling through the sistered joists was allowed. Any thoughts? Would we still follow the 1/3 rule, so nothing bigger than 2" holes for plumbing ?
Plumbing through sistered joists
- Thread starter Mopo
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wwhitney
In the Trades
If your sistered floor joist spans now comply with the applicable span table in the IRC (e.g. Table R502.3.1(1) where they are carrying bedrooms), without any credit for being LVLs or full dimension, then I would say the normal IRC rules for holes apply, the sistering doesn't matter. [Prescriptive method.]
up.codes
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However, if a design professional selected LVLs for the extra capacity, and did calculations to show that full dimension 2x6s plus LVLs are sufficient for the spans and spacing (which you didn't specify), rather than relying on the tables, then the question needs to go to that design professional. [Design method.]
Cheers, Wayne
Chapter 5 Floors: Floors, 2020 Minnesota Residential Code | UpCodes
UpCodes offers a consolidated resource of construction and building code grouped by jurisdiction
up.codes
Chapter 5 Floors: Floors, 2020 Minnesota Residential Code | UpCodes
UpCodes offers a consolidated resource of construction and building code grouped by jurisdiction
up.codes
However, if a design professional selected LVLs for the extra capacity, and did calculations to show that full dimension 2x6s plus LVLs are sufficient for the spans and spacing (which you didn't specify), rather than relying on the tables, then the question needs to go to that design professional. [Design method.]
Cheers, Wayne
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