Rafter insulation and soffit dam installation
> Hi Martin:
> I am a devotee of Fine Homebuilding Magazine and Green Building Advisor and greatly appreciate your expertise and devotion to what you do.
> We are building a log home in SE, British Columbia – Climate Zone 5.
> Roof structure – 14″ I-Joists, entire roof strapped with 2×4″s (cold-vented 2″ airspace),
topped with 5/8″ Sheathing, Titanium UDL 50 Roof Overlayment
> ridges, rakes, eaves covered with Grace Ice and Water Shield
12″ standing seam metal roof – with a CONTINUOUS Ridge Vent (RED LINE F)
we will be installing perimeter soffit around the entire roof structure.
Please refer to the attachments above:
1) Soffit Dam Photo:
Can you please advise the best method to seal and insulate the soffit dams between the I-Joist Rafter Tails? Plywood(interior/exterior/both) – 2-4″ EPS foam panels Cut to Size – applied to the Exterior, Interior or Both Sides? OR a combination of plywood and foam – of course – any/all remaining small cracks/openings to be sealed with foam and caulking.
2) Ridge/Rafters Photo – 14″ I-Joists – 24″ Centers – TOTAL R VALUE APPROX: R 48-50.
Our plan is to a insulate this deep joist cavity using a rigid foam-Roxul-rigid foam sandwich (RED LINE C)
1) Install 1″(R=2.1) Type 1 – SR12 Amvic Silverboard along/under the I-Joist flange along the entire rafter length creating the 2″ ventilation channel – (RED LINES A & B)
2) Install approx 11.0 inches of Roxul Mineral Wool in the I-Joist Webbing Channel (RED LINE C) approx R=46
3) Cover the entire bottom of the I-Joist a 1″ cap layer of Amvic Silverboard Type 1-SR12 (R=2.1) – (RED LINE D)
4) This layer would then be Air-Sealed with 6mil poly (Note: not visible in this photo – but 6 mil poly has been draped over the entire length of each roof purlin) – all seams overlapped by 6″, sealed with acoustical caulking – all seams taped. NO POT LIGHTS IN CEILING. Foam panel edges/cracks would be foamed and taped. We would finish the interior ceiling into the conditioned room by strapping the foam with 1×3”s and covering with 5/8” drywall.
Please note: the roof footprint is quite large – we will not be able to use spray foam – due to cost and lack of qualified applicator’s in the area.
If you can review and critique this plan and offer any suggestions it would be greatly appreciated!
Thank you for your time.
Cell: 604-613-5433 Delta , BC , Canada
Mark Kozlowski – B.Sc, B.Ed (McGill)
Life-Fec Consultants Ltd.
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