I am rebuilding a room in my house (built in 2007, in Michigan). Turning it into an office. As such I need to add additional wiring in the East (exterior) wall of the room. I can either cut the drywall and patch. Or pull the drywall completely and add 1/2” or 3/4” foam on the inside. Then cover with drywall.
This wall is 2×6 with fiberglass insulation. It has uninsulated headers over the window. The wall is 9’-6” wall but the wall is built as if it was 9’ with a BUNCH of 2×6 added to the top so with top plates plus this pack out it has something like (6) 2×6 stacked on top of each other. For about a solid 9” of “top plate”. (I have NO idea why it was built this way)
The question is. Is it worth taking off the drywall and adding the insulation? The thermal bridging of the 9” of wood is pretty noticeable if you touch it in the winter. Note the outside is vinyl siding with house wrap over plywood.
if it matter the header is 8” tall. So 6-8 to 7-4aff is the wood header, 7’-4” to 8’-9” aff is 2×6 studs and fiberglass and 8’-9” to 9’-6” is solid wood.
This room is on the North East corner of the house and will be my home office, I work from home so this room is occupied more then any other in the whole house.
So any suggestions?
Replies
I would not tear it apart to add 3/4 inch.
It would make sense (to me) to pull the wall and plan another 3. inches of rock wool. could frame at right angles to existing studs, or at a different spacing.
I would look at both exterior walls. sound reduction benefits could come into play, if the windows are good enough to help.
(is a leaf blower during a client call a concern?
Sound is not a big factor, and that wall faces the back yard (i live on acreage) and this has less noice issues then the north wall. (which i don't need to rewire)
It is mostly the bridging issue that i wonder about. I can clearly feel the huge temp. difference at the top of the wall where all the 2x’s are stacked on top of each other with no insulation.
The R-value of the fiberglass should be 19-21 the R value of the wood is about 6-7. and between the header the sill, the bottom plate and the number of “top plates” about 1/6th (or about 1/4 when you add in the studs themself) of the wall if wood. That is a lot of area with no insulation to speak of.
Doing the math 27% of the wall is solid wood. (more then a typical wall would have) 73% is insulated.
Insulating with 3/4” foam raises the r-value of the 27% to about 10-11 a close to that of 2x4 fiberglass. And raises the rest to about 23-24. I just don't know what the truly means beyond the basic math.
If i go with 1.5” that is even higher.
I would look at an interior soffit covering the solid wood build up area. Add insulation as required in the soffit. Would also help the typically cold wall ceiling corner. Dry wall behind the soffit should be cut back to tie in a vapor barrier around the extra insulation.
The soffit could also provide space for any additional HVAC service, accent or task lighting, electrical or low voltage cable runs, etc.
Run the soffit around the room to create a tray ceiling.
And, as was suggested, the soffit could be used as your wire chase, which also would allow you to snake your wires from there inside the wall down the bays, without having to cut any drywall out (except for your new receptacles). Good idea catmandeux, if he likes the look of a soffit.