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Question DetailsAsked on 2/15/2018

insulating garage that already has drywall and some insulation in the wall and ceiling

The ceiling is below my living room/dining room area and one side wall goes into my laundry to den area. I was considering insulation options that would hopefully not require me to pull down all the drywall and ceiling and reinstall insulation if I can avoid it. Could I use R board or are there other options? What would be most cost effective?

Second to this is my garage door leading into the house, the original door is from 1974 so I suspect it is not the best insulation. What would you recommend as a replacement and what other steps do I need to take to insulate in teh door area.

Lastly, in the laundry area the back wall is cinder block, so I suspect this is a heat loss zone. I don't think there is enough space to frame the wall since that is where the washer dryer and utility sink sit and the exit door into the garage won't leave much space to build out a back wall. Again, would R board work well in this case?

Any other tips or areas I should look into

Thanks for all the advice!

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1 Answer


Assuming this is a cold or cool garage (not maintained at house temperatures), otherwise why would you be looking for more insulation.

Without looking in the existing walls/ceiling with a fiber optic scope (takes about 1/2-3/4" access holes in the drywall which would need to be patched for fire safety), no telling how much insulation or what type you have - if fiberglass batting, likely (at least if 2x4 construction) might not be any room for insulation. if 2x6 or 2x8 floor joists in the ceiling there might be or might not be room in there for more. Scope rentable for $15-20/day for handheld scope, $20-40/day for digital type with about a 3-4" display screen, at Home Depot, tool rental places, some auto parts stores.

To add insulation, if there is space for it, you can use blown-in fiberglass or cellulose insulation (latter one not at all a favorite of mine - packs down badly, absorbs moisture, rodents and insects love it) or foam-in place insulation (typically double to triple the cost) can all be used. Of course, means some holes in the drywall (typically 3-4") which would have to be patched, but avoids tearing the drywall out. Can also be done (actually probably better job) from above if carpeted floors which can be rolled back to expose the subflooring to inject it through - but somewhat messy as there is a fair amount of dust if blowing in fiberglass or cellulose - foam not a problem.

RBoard (now called Atlas Energy Shield CGF) is a rigid foam board - hence quite highly combustible, actually quite flammable burning very much like napalm once it starts melting, and puts off TONS of deadly gases and smoke when it burns. In building fires involving exposed foam insulation (remember some nightclub fires with sprayed-foam decor or ceilings cathcing fire at concerts ?) fatalities are usually suffocation by the smoke and gases put out by it long, long before people get burnt to death - sometimes occurring almost before the smoke alarms go off. Saw one aircraft hanger with exposed foam board insulation on the walls go up to TOTAL engulfment in less than a minute from a welding operation ignited fire - anyone in there after the first 30-60 seconds would have been history. Fortunately, was single-story and wide open rolling doors at each end so the workers got out, but not without some serious injuries.

If you remember the Grenfel Tower fire in London last summer which killed about 70 people because of fast-burning foam-core facade material, RBoard is basically the same material as that without the metal facing. Hence, cannot be exposed inside the house in the US or most of Europe - needs fire-rated (Type X) drywall or similar fireproof covering - minimum 1/2" thick, almost all areas 5/8" Type X required on ceilings and in some areas up to 3/4" under living spaces like your case. See local code requirements for details.

There are fireproof/highly fire resistant pressed fiberglass and rock wool (like fiberglass but made of "glass' made from rock, looks much like the old asbestos board except usually yellowish) board products out there which you can put a thin drywall or architectural surface (typically 1/4 or 1/2" thick) over - decent but not great insulation, more similar to batt R values, and lousy insulation if it gets wet. More expensive ones come with a metal facing ready for interior use - called insulated architectural panels or such.

Here are a couple of links to articles by manufacturers on putting drywall over combustible insulation:

Inside the garage, you could, in most areas, legally put foam board over the existing drywall, then overlay with another 1/2" / 5/8" drywall layer on walls/ceiling respectively. Have to take special steps to isolate the foam from any fire exposure at all wall/ceiling penetrations, using fireproof expansive firestop sealant and/or metal fire shields, but that is a minor added cost and effort for your case - not many penetrations, and most are small. Also requires resetting the light and switche boxes and such so they are not recessed several inches, and requires wood bottom sill strip under the insulation board so it is not exposed at the floor. And of course, putting it on the garage walls loses you a number of inches of garage dimension in each direction - and if a low ceiling garage might cause problems there for SUV or pickup access too.

Garage entry door - if this is a "cool" garage - not house temp but not below about 40 or above about 90-100, I would not worry if this is a typical solid core wood door (cannot be hollow-ore by fire code). If garage is truly outside temp and you have cold winters or scorching summers, then there are insulated fire-barrier doors you can buy - usually metal-clad (100% coverage) over foam core - typically about $200-250 for a cheap one, plus installation which if same rough opening sized, probably close to or about that much again unless you can DIY. I would not worry a lot about heat loss through the door itself unless you have extreme garage temps, if even then - pretty small surface area for het flow to go through compared to the expanses of garage walls, and any legal fire-rated garage entry door is going to be far better then say equivalent window glass area in the house, and usually just sealing around the door and around the doorframe saves you a lot more energy than a better door itself will - and also has the added benefit of increasing fire safety in the event of a garage fire.

Use fireproof foam-in-a-can or fiberglass insulation to insulate around the door frame (under the trim), and use bronze nail-on sealing strip on the door jamb like this - comes in strips and rolls (I recommend rolls to minimize wastage):

Note if sealing the garage rollup door with vinyl or rubber weatherstrip, which can change the garage temp a LOT, using products like links below, if there is a furnace or water heater in there be sure you have adequate makeup air intake area via exterior wall vent, because they will not be able to get makeup air via leakage around the garage door any more.

Laundry room - if you do not have room for at least about 3 inches of insulation, your options are foam board (R value about 4.5-5 per inch thickness for expanded polystyrene, 5.5.7 for more expensive fancier polyiso and such - so a couple of inches is roughly equivalent to 3-1/2" of normal fiberglass insulation. Can be construction adhesive glued to block wall, then put in 1/2" Type X drywall over it for about half as thick an overlay as with a normal 2x4 studwall. This assumes of course this is a "dry" wall, without outside water seepage issues, which would have to be solved first if they exist, which would naturally lead to the next paragraph solution instead.

Another solution for that laundry room (assuming the "back wall" you are talking about is an outside wall) is digging down on the outside of the wall (carefully, to avoid damaging any waterproofing on it, and watch out for buried utility lines) and laying up closed-cell insulation board like Dow Hi-40 (my preferred brand) to the desired R value - preferably 2 or more layers so you can stagger joints to avoid "short-circuiting" through the joints. Terminate 3-4 inches BELOW ground level because insects like nesting in it - so not a great idea in termite country unless you overspray with thick asphaltic/bitumastic waterproofing. (In termite/carpetner ant/post beetle country I prefer to have a pest control contractor spray treat the insulation board with a residual insecticide spray before putting the spray-on waterproofing over it).

One other thing I have seen on back walls in utility rooms like that - cheap and dirty - is using metal firring strips to loosely fasten roll water heater/rollup garage door insulation blanket across the block wall. Not pretty, and facing has to be fire-resistant (as those two types should be), but quick and easy to do. Even just running a firring strip top and bottom with nothing in the middle can handle a typical utility room sized wall. And of course will not handle rough handling.

Other tip - look first at air leaks in the house - then at limiting door and window losses with weatherstripping, and tight-closing blinds or insulated curtains on windows/sliding glass doors, and insulated foam sealer pieces at wall outlets and switches, and losses into the attic around penetrations and any access hatches/doors - you can commonly make as much difference in total energy bill by sealign up air losses as by doing a major insulation upgrade.

Answered 2 years ago by LCD

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