Saturday, April 3, 2010

MAISON GRANDE-DIGUE HOUSE - Roof @ Kitchen Extension

Roof trusses at kitchen extension are raised heel trusses to allow for 18 inches of glass fiber batt or blown insulation (R60). The roof trusses are installed at 24 inches on center in line with wall studs below. 6-mil vapor barrier is attached to the bottom chord of the truss. Gypsum wallboard or other desired finish is attached to the truss chords on 1x4 furring strips at 16 inch on center perpendicular to the trusses.

The benefits of installing radiant barriers are still in question. If used, I would recommend attaching the radiant barrier taping all joints to the bottom chord of the trusses after installing the vapor barrier, but prior to installation of the furring strips.

Roofing material is TRACC Moderne Slate roof shingles over ice shield underlayment. This is a 50-year roofing material made locally from recycled materials capable of withstanding a 175 mph wind driven rain. This is a very important feature on the Northumberland Strait where northeasters are not uncommon. The roofing sheds snow easily so consideration must be given to sliding snow in our climate. The roofing also works well for a rainwater collection system (guttering not shown).

Maison Grande-Digue House is designed with double 2x4 insulated, exterior stud walls @ 24" o.c. separated by a 3-1/2 inch fully insulated space to isolate the exterior walls from thermal bridging. The outside double stud walls would be erected prior to construction and erection of the interior stud walls. The inside stud walls are designed to be load bearing while the outside stud walls are designed to carry the exterior finish. The cold side of the inside stud wall is completely covered in a 6 mil vapor barrier then sheathed with 1/2 inch CDX plywood sheathing to provide lateral bracing as well as protect the vapor barrier.

Red dashed line shows location of the 6-mil vapor barrier in the wall system. Red dots show locations where barrier is sealed with acoustical caulking.

Experience has shown that the vapor barrier can be safely installed inside the wall as long as 2/3 of the insulation is on the cold side of the barrier. Locating the vapor barrier at the cold side of the inside stud wall allows for installation of electric without penetrating the vapor barrier. The cold side of the outside stud wall is sheathed with 1/2 inch fiberboard sheathing, then covered with house wrap. The design allows for the walls to be framed and insulated on the floors and lifted in place using wall jacks.

Details for optional balloon framing and openings are provided in the links and will be discussed later.


Radiant Barrier said...


I enjoyed your post and you are certainly knowledgeable. Why, out of curiousity do you question the effectiveness of radiant barriers as a product that can increase the effectiveness of the overall unit?

Karl said...

This shows what can be done with traditional timber. All designs are compact and utilize highly efficient space arrangement for keeping heating costs down. Its great to see how you make the most out of standard sized and commonly available lumber.
This is truly futuristic and affordable housing of the future whilst maintaining a traditional look.
Great work.
Karl from Hobart, Tasmania