Double Stud Wall section
Although there is a lot of discussion and recommendations for double stud walls (R40) filled with dense packed cellulose walls on GBA, I could find no diagrams of a recommended wall assembly in your strategies and details section.
We are in the preliminary design phase for a two story house in Upstate NY (2,200 sq ft – first floor 1,500 sq ft), second floor 700 sq.ft.) (Zone 5a) built on an insulated (R20) floating slab and plan to have a vented roof (R60) with raised heel trusses over the two story portion of the house. I would like a sloped roof over the single story living area.
Is an internal or external load bearing assembly better? My builder says 2×6 are required for the outside wall, we can use 2 x 4 for the inside wall.
Recommendations on whether to use closed cell foam and where, exterior foam, sheathing type, etc.? Window details would be nice too.
I am looking for an effective and cost efficient design. A detailed wall section would be very much appreciated.
thank you
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Replies
Liz: There is no one way to do double stud walls. Search here, buildingscience.com, and Google various terms and I think you'll find what you seek. Terms like double stud wall, Larsen Truss, Riversong Truss, the Sunrise House (here), etc. Thorsten Chlupp may have made public his flavor of double studding w/ plywood on the outside of the inner wall as an air barrier. Google him, too.
Elizabeth,
GBA is now working on adding double-stud wall details to our detail library. In the meantime, here are some links you might find helpful:
Double-stud walls
Best wall construction for long term efficiency & durability
Airtight Sheathing & Thermally Isolated Double-Stud Walls?
Choosing a High-Performance Wall Assembly
Is Double Stud-Wall Construction the Path to Efficiency on a Budget?
‘Innie’ Windows or ‘Outie’ Windows?
Martin,
That's great news about the GBA details
What is the "status" of the GBA Double-stud wall details?
Are they in the process of being drafted right now?
Do you think they will be posted in a few days? or in a few weeks?
John,
Q. "What is the "status" of the GBA Double-stud wall details? Are they in the process of being drafted right now?"
A. They have been drafted, but they need to be checked, edited, and formatted.
Q. "Do you think they will be posted in a few days? or in a few weeks?"
A. In a few weeks, we hope.
Martin,
Gee I wish it was coming out sooner. We are meeting today with the architect and builder to discuss our wall structure (Integrated process - I'm the GC, builder will be my construction manager). Can I send you what we come up with?
Elizabeth,
Many GBA readers post plans and details on our Q&A pages to invite comments. And many readers have found the process useful.
I used the outside wall for support and it was 2x4 walls for both, these were 2 story homes. Framing was 16" oc and double top plates. The inner wall (non supporting wall) can use a single top plate.
Elizabeth,
There are some details for a truss wall assembly with airtight sheathing on my blog, maybe you will find them helpful:
http://ourhouseuponmoosehill.blogspot.com/
The service cavity isn't for everyone but there are many advantages to this style truss wall.
I have just finished framing the exterior truss assembly and found it to be a very "buildable" approach - I built it by myself after all.
The double wall Habitat For Humanity house in Golden, Colorado is a very straight forward design.
http://www.nrel.gov/buildings/pdfs/43188.pdf
Hire a good builder, this is the best money you will spend on a new home.
Doug,
The question is whether 2x4 16 inch on center is less expensive for the outside walls than 2x6 24 inches on center? Any other building considerations with either option?
Elizabeth,
I like 16" centers personally, I would say it's a wash between the 2x4, 16" and 2x6, 24" in terms of cost or board feet used.
Doug: Don't people generally use 5/8" sheet rock w/ 24" OC? If so, that is a small consideration.
Liz: up here, two 2x4's are cheaper than one 2x6. That, with the plates, makes 2x4 far cheaper, if applicable. Check local prices.
Here's a detail from a recent HERS 15 home just completed. I agree with using 2x4's for both walls. The issue is if you have a lot of foam on the exterior of your slab it can impact the bearing of the exterior wall and I like to make the exterior wall the load bearing wall so all my headers are to the exterior. In this home we used a block wall with a floating slab and an embedded galvanized termite flashing/ moisture barrier detail. So we had three inches of foam between the slab and the block wall and could have our exterior wall bear fully on the block so it was fine to make it a 2x4 wall.
As Martin says, there are many different ways to do it. I like to frame the inner walls separately from the exterior walls and connect them with a horizontal purlin at mid span. I also like using a 2x10 (or 2x12) solid lumber upper top plate. We use an airtight drywall detail not shown on this drwg that has a strip of poly laid between the two 2x4 top plates and the 2x10 upper top plate which is then taped to the house wrap on the exterior of the house and folded down on the upper top plate and held there by the drywall gasket that is compressed when the walls are drywalled.
In this house we also used a solid PT lumber bottom plate which makes caulking the plate to the floor slab a lot easier than if you have to caulk the exterior bottom plate to the slab and already have the interior wall up and "in the way" We do frame our walls 24" OC and use 1/2" drywall on them and have been doing it this way for thirty plus years. Only time I use 5/8" drywall is on ceilings when the ceiling joists or trusses are 24" OC. Think about what makes drywall wavy- Bowed studs. Thicker drywall doesn't prevent bowed studs.
We recently built a house with a double wall system and used 2x4 walls on 24" centers (meets our local code requirement) with an exterior load bearing wall. We used 2x4 top plates but connected the two walls with 12" wide pieces of 3/8" plywood top and bottom running the full length of the walls (like another top and bottom plate) and attached 12" wide pieces of plywood mid-height to keep the wall width consistent. We used 1x4 for the bottom plates because with the addition of the two 3/8" pieces of plywood (3/4"), making the bottom plate 3/4" thinner kept our total wall height the same as a standard wall, allowing us to use standard stud length studs and drywall. After experimenting, we concluded it was fastest to build the two walls together on the ground (connected with the top and bottom plates) and stand them up as a single unit. There are lots of great options, but we were happy with this and would do it again.
It may be simpler if not the most energy efficient to think of the inside 2 x 4 wall as just an interior wall. It only needs to line up at windows and doors and otherwise is laid out for sheetrock like any other interior wall.
Michael Chandler - I wonder if you could try re-posting your detail from yesterday - I am not able to read any of the notes on the version that is there now. We have built several double-wall homes here over the past three years and are always looking to improve on the margin. Many thanks.