Eichler house roof adding 6 inches of insulation, roofline ideas

[Bill Dufour]

We looked at a few Eichler type houses and wonder how to add foam insulation to the roof without it looking clunky. These have exposed rafters about four feet apart with 2x6 tongue and groove on top for the ceiling and the roof deck with no insulation. R33-40 is recommended here. That would add 6-8 inches of foam plus plywood to the roof line.
So you could fill up the ceiling gaps and drywall over the wood ceiling. On a flat roof they apply spray foam but on low slope with shingles they say apply foam board insulation and build up the eaves to match. I think it might be interesting to make it look like the tudor roofs with a fake straw roof edge treatment.
Has anyone ever seen something like that or have pictures. I do know any ceiling wiring has to be done before the roof goes on.
Bill D.


http://www.boyenga.com/mountain-view-eichler-neighborhoods.php

https://www.zillow.com/homedetails/1312-Edgebrook-Dr-Modesto-CA-95354/16067723_zpid/

https://www.customshingles.com/false-thatched-roofhttps://www.customshingles.com/false-thatched-roof (https://www.zillow.com/homedetails/1312-Edgebrook-Dr-Modesto-CA-95354/16067723_zpid/)

[Jamie Buxton]

Often Eichlers have long overhangs. There’s no purpose in insulating them. So you put insulation on top of the existing roof, but taper it down near the edges of the roof.

A bigger issue is what to do about heating. Eichlers here have hot water in the slab, but often the pipe is iron, and it has rusted closed. So folks put in forced air, with ducts on top of the roof. If you’re concerned about a few inches of insulation, you likely won’t like 15” tall ducts on the roof.

[Bill Dufour]

You have to have ac here in summer. I will have to make sure any house we buy has ac and heat that works. Thanks for the information.
Bill D

[roger wiegand]

On my son's house, a MCM from 1960 similar in concept to an Eichler (very low slope roof, really stupid in New England) I was able to find and re-use foam slabs removed from a commercial building. We put 8" of closed cell foam on top of the existing roof sheathing and then put a rubber roof on top of that (it's not visible from the ground, so looks were not a concern) The foam cost about $400 from the recycler, so a real bargain and the performance has been great, his heating and AC bills are minuscule.

All the houses on his street were identical when built, his has a wider fascia board than the others, but no one would pick it out as being odd or of proportion. It's the blue one on the left, compare to the original thickness on the white house on the right.

444150

[Frank Pratt]

On my son's house, a MCM from 1960 similar in concept to an Eichler (very low slope roof, really stupid in New England) I was able to find and re-use foam slabs removed from a commercial building. We put 8" of closed cell foam on top of the existing roof sheathing and then put a rubber roof on top of that (it's not visible from the ground, so looks were not a concern) The foam cost about $400 from the recycler, so a real bargain and the performance has been great, his heating and AC bills are minuscule.

All the houses on his street were identical when built, his has a wider fascia board than the others, but no one would pick it out as being odd or of proportion. It's the blue one on the left, compare to the original thickness on the white house on the right.

444150

I would argue that your son's house with the wider facia has better proportions than the neighbor's house.

[Bill Dufour]

I agree the wider facia looks better then the original. I was concerned it would look clunky. They must use really long screws to hold it all down. I was concerned a big almost flat roof would heat up the house when it is 110 and sunny for days on end. probably take some time to find a experienced roofer for this kind of work. I bet the foam will cost more then the shingle job.
Bil lD

[roger wiegand]

The roofers used special washer head lag screws about 12" long with a 3" washer to hold the foam down, the screw heads were recessed so no sharp edge to contact the rubber roof membrane, basically exactly the same as for a commercial building roof. Do look for foam recyclers; apparently it is standard practice to replace the foam when doing a commercial roof replacement. They had some in ratty condition from leaking roofs, but the stuff we bought was pristine. It was polyisocyanurate foam with fiberglass backing.

[Walter Mooney]

Bill,
Back in my days of building log homes in TX, nearly all of which had exposed t&g decking in the cathedral ceilings, I insulated the rooms from the top. We'd put felt paper on top of the t&g decking. We would run 2x4s (or 2x6s depending on the insulating value the client wanted) on edge, up the slope, screwed to the purlins (almost always logs) with screws similar to what Roger described -- 8" or 10" self-drilling lag screws -- 3-1/2" through the 2x4, 1-1/2" through the t&g and the rest into the purlins. These 'rafters' were run at 16" o.c. Electrical was always installed at this stage. Then, in between these 'rafters' we put rigid foam board insulation, either 3" or 5" (depending on rafter depth), ripped to 14-1/2" wide. Then we'd deck the roof with radiant-barrier plywood or osb, with felt paper or ice and water shield, followed by whatever the roofing material was to be (shingles, standing-seam metal, etc.). There would be 1/2" or so gap between the top of the foam and the bottom of the roof decking. We put ridge vents at the ridge and soffit vents in the underside of the eaves. This allowed for passive air flow up through the entire length of the roof, from bottom to top, since hot air always rises, whether it's summer or winter. The combination of passive venting of the roof and the radiant barrier decking gave "effective" R values significantly higher than just the R value of the foam! I had great success with this!

Best of luck with however you choose to do!

[Bill Dufour]

Adding the upper rafters sounds like it about doubles the roof cost. I know with the flat roofs many were built with no venting of any kind. But I think being where I never get ice on the roof makes a difference. The classic idea of a cold roof seems to be under debate now a days.
Was the purpose of the upper rafters just to add a vent space instead of using solid foam with no vent channels?
Bil lD

[Walter Mooney]

Bill, that roof design accomplished several things, including adequate insulation, passive venting and increasing effective R-value of the roof insulation by way of the venting and the radiant barrier decking. The number of times per year that any of my log homes got ice on them might be one, maybe two. But the number of days per year where the temps are in the 90’s or more are more than one would care to count!

[Bill Dufour]

most of June and July was over 100 each day here. Another hottest summer on record.he more insualtion the better

Bill D