Monday, July 14, 2014

A Skylight Insulated >R30, With Plywood Hard-Covering

My first trial of hard-covering a well-insulated skylight is continuation of work reported in this blog post:
Daring To Collapse and Rebuild Crummy Loose-Fill Fiberglass Insulation 

This skylight in a far corner was reached, with displacement of the surrounding floor insulation, when an adjacent bath fan was replaced. A non-contact draping of R11 kraft faced batts, has had no insulation value.

Here is framework attached to the skylight. Employ 1/2" plywood and 2x2 to enclose from above, with a 7 1/2" insulation thickness and a minimum of framing thermal shorts.

Note materials now ready to clad the skylight. I have stripped the kraft facing from found insulation and will set it to fill the 1 1/2” depth of side on-flat 2x4. Rumpled kraft facing prevents intimate contact against drywall and is harmful, absent a base layer of conforming  loose-fill. Facing is select 3/8" plywood. The sides are from one diagonal cut of 24" width plywood. The face has attached 2x2 edge nailers.

All found insulation is reset, stripped of kraft facing. A full covering of new R25 batts is needed to fill the space of framing for the plywood covering.

Done at the skylight except for a third layer of insulation on the floor, R25 covering all 2x4 truss bottom elements, floor total about R46. For now, the floor is generally R10, and demanding improvement.

Is this what a skylight should look like, from the attic? Know skylight shaft area near roof sheathing is still not insulated. I could stuff some in above the plywood. Should I? I won’t, protesting that skylights in shafts are not windows, a bit inefficient and weird now. I will prefer LED lighting.

Plywood temporarily set on these truss bridges to the skylight, has been taken away. I will use access under these bridges to complete the sealing and insulation of the attic floor, before fitting and setting a permanent walkway. Home builders should make their work easier, and access safer for anyone, by including such level walkways. The bridges and an anchored walkway are beneficial to truss stability.

Suspicion about insulation at the back wall of the skylight was justified. A negligible kraft faced R11 batt was set, not in contact with the drywall and again having no insulating value. A careful cutout, full stuffing of insulation and drywall patch with flexible grout  took about two hours, of nine  hours total spent in insulating the skylight.

Payback Math For R30 Attic Wall Insulation: This skylight has insulation area 30 sf, of total 220 sf attic walls. The cost of all  attic wall insulation was $890; and that of the skylight was $175. Deduct a $.30 per sf rebate, $66, for all walls net cost of $824. Savings for insulating 220 sf from zero to R30 are $2.4 * 220 * (1/3-1/33) = $160 per year. Payback time is  824/160 = five years. R30 hard-covered insulation of attic walls is a very good investment.

Please find details of all attic wall insulation in this home, with concurrent attic floor sealing, in a pdf photo album:

Insulation and Hard Covering of Attic Walls

1 comment:

Thiago daLuz said...

My brother is going to be helping us install some new insulation this month. Our old stuff just isn't going to cut it for another winter. We are probably going to go for a bit of an upgrade from our old stuff. Thiago |