1953 unfinished attic floor, storage, retro install; overkill?
It looks like we’ve got R9 and want to get up to a total of R49 rating. There’s lots of good storage space with solid wood flooring on the attic floor joists. We hate to lose all that space (and especially if we resell think it’s a selling point) to blow in. I’m looking at DIYing but find so much contradictory information and opinions online it’s hard to sort it all out to a novice and first time home owner. I will tell you where I live we’re in zone 6, so it does get cold here. And it does get warm in the summer too, so we want to insulate against summer heat on roof and to keep cold in from a/c in summer AND more importantly keep heat from escaping given the little bit of R9 there now.
We also only have a carport and shop in the back with no garage so storage room/space is at a premium, so we hate to lose some of the only storage space in the home there is by blowing in, which is what my general contractor friend strongly recommends (and he said go to R38 but after researching online, we really ought try to get to R49).
I’m so ignorant I may sound stupid to some of you, so please be gentle; and all of the contradicting information on the web makes me feel totally lost and confused. One question I have is if we know we have R9, does that mean if our goal is R49, we need to add 40 R (whatever the material), or at least 29 to get to R38?
We’ve seen several threads recommending what I believe is known as poly iso insulation decking (but it appears that usually goes on the outside of roofs under sheathing or commercial installs, or on the attic “ceiling” although we do see a few google image searches where we see double-decker 4″ attic floor installs.
We think this could be a smart solution to our unique dilemma (having so little storage space at this property over all, not wanting to lose that little extra).
So I see other people say elsewhere on some threads to install reflective styrofoam installation between the top truss chords underneath the plywood decking (mostly for energy efficiency to reflect solar absorbtion in summer time), which may be a smart thing for us to do for said reason given our wishes. And it might help minimize some heat loss too, although the bulk of that would be from sealing air leaks (if there be any) and insulating the attic floor.
So here is what I’ve envisioned to preserve the storage space and at least get better insulation.
1. put foam or plastic rafter baffles between truss chords for soffit vents OR use rigid styrofoam board to create soffit chutes at roof edges only
2. install rigid styrofoam insulation as a radiant barrier with white side facing roof and metallic side facing attic floor, which might eliminate step one by creating the chuttes which will protect air flow to soffit vents and avoid ice damming
3. blow in to corners of attic to where webbing supports start, and then use styrofoam boards to contain the blown in on both sides to a four feet center margin exactly (or install some, and then blow into space), preserving a four foot width for the poly iso decking to use double deckers);
4. once entire roof is done with rigid styro into rafters on roof, and blown in is done into corners, then bring in the poly iso insulation decking 4″ sheets and double decker it, and at edges of double deckering, then use some kind of spray sealant for the joint between the double stacked decking and the R23.6 poly iso 4″ decking
Yes, I know that’s more expensive and MORE work than just blowing the whole thing in, and in some ways redundant, but here I see that I’d have radiant heat protection/barrier to keep the whole house cooler (no shade on it from outside) due to higher elevation direct UV and sun (very sunny in summer usually all summer) which will preserve A/C bill and carbon waste. And the rigid styro foam radiant barrier rafter chutting will preserve the roof from ice damming WHILE serving as radiant barrier in summer and allow the edge blow ins rather easily without worry of clogging venting. (rigid radiant barrier installed on rafters). And then the decking with seal would preserve storage space and with a double R23.6 plus the R9 existing with the edges at the rigid styrofoam walls holding the blown in corners perpendicular to the attic floor being sealed with some kind of spray foam, it would minimize the chance of ice damming from differential heat leaking.
Yes, more expensive, yes more labor. Yes lots of cursing. BUT in the end, I think it will pay off over time in saved energy and less carbon footprint. It is a 1896 square foot house and we’d never intend to finish a room in the attic. And then too the gable vents and passive roof vent (in addition to soffit vents) would all work together to still prevent ice damming, and with a radiant heat barrier AND thermal attic roof floor barrier would also keep the house in general cooler in summer.
Is this overkill? What are my risks besides to my pocket book?
It would also seem with the blow in option and radiant barrier/chutting and double decker insulation decking to me that air leak cealing from the home into the attic would be moot given the blown in R value getting up to R38/.49 would solve the problem at edges, and the solid decking with sealing at its edges would also eliminate heat leaks through the roof that way too.
My realtor insists we’ll lose more heat from doors and windows than we will wasting our money retrofitting the attic insulation. My contractor friends says my realtor friend is stupid. There is a basement walkout door and front door and side door. All windows aren’t original but are double pain and pella and seem installed well. Vinyl siding too; not sure how well insulated walls are, and really don’t want to plastic wrap my windows as despite my allergies, I’d like to turn off the air and heat (even in winter) and get fresh air inside (plan on installing hepa material in all screens). And maybe next summer, I’d work on replacing those doors. The front door seems like solid wood (they don’t make them like they used to), but the basement walkout door seems like a standard foam filled door, as does the side door. If I just made sure the weather stripping around them was tight and that the latch plate is installed tight (plan to install latches), that would deal with some of the energy loss, yes? And windows seal tight although are not triple paned and probably will never fix windows nor do I want them to be plastic sealed shut. But I do have a friend with a house of similar age and what he tells me his gas and electric bills are without plastic sealing shut, I shudder to think what my budget looks like next year. Hence ounce of prevention talk now please.
So, your thoughts please? I know that’s A LOT A LOT.
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Your description is hard to follow, so I'll provide some general guidance.
1. In most cases, investing in a radiant barrier is a waste of money, although it's certainly possible to use foil-faced rigid foam to make site-built ventilation baffles if you want. If you do that, the foil should face the air space (the ventilation channel). For more information on radiant barriers, see Radiant Barriers: A Solution in Search of a Problem. For more information on site-built ventilation baffles, see Site-Built Ventilation Baffles for Roofs.
2. The easiest way to add more insulation to your attic floor, while keeping some room for storage, is this way:
(a) Temporarily remove the floor boards in the storage area.
(b) Add new floor framing above the existing floor framing, installed at 90 degrees to the existing framing. If you want to add 9 more inches of insulation, install new 2x10s.
(c) Blow in cellulose on your attic floor, up to the top of the new framing members.
(d) Reinstall the old floor boards, or install new plywood if the old floor boards aren't worth saving.
3. If you decide to create an unvented conditioned attic, you can install new insulation that follows the roof slope. Here is a link to an article that tells you how to do that: Creating a Conditioned Attic.
For energy, I'd advise looking for air leaks and sealing them before adding insulation. Then most added insulation will work.
My concern is structural. In 1953, the joists might be stout enough to handle the ceiling load plus the storage load. But if the joists are 2x6 or less, and the ceiling is plaster rather than drywall, you should be judicious in designing for the storage load. I recommend running the new joists parallel to the exiting joists. They should be independent of the existing joists, and supported on the same bearing lines. You can do this by nailing a plate onto the existing flooring at (or close to, at the eaves) the bearing wall or support, then running the new joists from plate to plate. That way the storage load is not transferred to the joists supporting the ceiling. I hope that makes sense.
Bill Rose's points are spot on. You should listen to him.
For more information on attic air sealing, see Air Sealing an Attic.