Foam board under siding ??

[c6matt]

I have my framing starting on my 30x48 garage next week so I want to get my plan together for the insulation. it has 2x6 walls, 12' cielings. I plan to heat the shop all winter @40°F using a radiant tube heater powered with nat gas. Outside will be tyvek wrapped osb walls with vinyl siding, interior walls will be drywall with a ribbed steel ceiling.

The two options I was looking at was

1)R19 Fiberglass Batts in the walls and R30 in the ceiling, R5 foam board under the siding

2) Spray in foam 3" walls and 6" ceiling for the same R19/R30. But with that setup would I still want/ need the foam board outside? Is heat loss through the 2x6 studs a concern?

 

[sands35]

My shop is 26 x 32 with r13 walls and r30 ceiling. Normally kept at 40*F, 50*F when I'm in there. I did not notice the increased nat gas usage from last year. Heat was turned on in January.

Given the typical day this past winter was around 10-20*F, a 40*F shop isn't that much delta T. So you won't use many BTUs to keep it there, so more insulation on the walls won't really add much to the insulation properties of the garage. The problem that I ran into was the thermal calculators are designed around an assumed 70*F interior for a living space, not a garage.

If you want to improve the envelope efficiency, pay attention to details around air sealing. Foam any holes in the sheeting, ensure the house wrap is well taped, ensure there are baffles in the ceiling insulation / soffit area, caulk or tape gaps in sheeting, foam doors and windows, etc. Putting the garage door in a wall that does not face prevailing winds. Basically ensure a wind proof shell.

You could add furring strips horizontally to the interior of the wall and that will substantially reduce the thermal bridging to the interior surface.

You can add foam to the outside. You will just need to find fasteners long enough to hold the siding to the wall sheeting or studs. (all I'm suggesting is that it won't help as much as it will with a 70*F house.) The basic idea of using foam sheet for the exterior is to put the dew point during a cold winter's day in the middle of the sheet - so that any condensation will not be able to form - hence keeping the interior wall space dry and mold free.

 

[c6matt]

This is very helpful, thanks!

With air sealing being a priority, that makes the foam more attractive. I was worried about conduction through the wood, maybe I am over thinking it. garage is sheltered from the wind by a tree line and the house, and my lot is heavily wooded.

What do you mean by this ? ensure there are baffles in the ceiling insulation / soffit area,

 

[NUTTSGT]

Matt,

Part of my garage is block. I have it insulated on the inside but when I sided it last year, I had to add some firring strips to attach the siding to. Since I was adding the firring strips, I decided it was a good time to add some extra insulation. For half the money of pink foam, I added some white styrofoam which gave me a few extra on the R-Value over nothing.

 

[c6matt]

Interesting Eric i could consider somthing in the middle...
, what do you guys think of this? Looks Like I could do the garage for ~$300
http://www.menards.com/main/buildin...ment-board-for-re-siding/p-1696358-c-5778.htm

 

[LB-1911]

What do you mean by this ? ensure there are baffles in the ceiling insulation / soffit area,

You should find this of use -

Air Sealing: Attic Baffles
http://blog.sls-construction.com/2011/air-sealing-attic-baffles

 

[c6matt]

Ah, so I would install this product and then have the foam applied. Does this just nail/screw to the sheeting? I imagine it would be easiest to install from the soffit side, before they are installed.
http://www.menards.com/main/buildin...4-x-48-plastic-vent-chute/p-137194-c-5776.htm


Thanks everyone, I am learning a lot, only want to do this once!

 

[sands35]

These go under the roof sheeting and tie into the top plate.

You want something that looks like this:
http://www.menards.com/main/buildin...ic-vent-chute-with-baffle/p-137192-c-5776.htm

Not the one you posted.

Do it like this:

http://www.epa.gov/iaplus01/technical/moisture/wind_baffles.html

They are stapled up to the underside of the roof deck after the garage is weather tight, but before insulation and wiring. Typically from the inside, so you can do it after siding is up. If you want to detail them well, use spray foam to seal the edges so that wind doesn't blow around them and into the ends of the insulation.

 

[WVBrady]

Under Option #1, wouldn't the foam board on the outside act as a second vapor barrier (a no-no)?

 

[Steve in Mi]

I used R=19 in my walls and 1" Dow rigid T&G foam on the exterior of my 2 x 6 on 16" centers covered with T1-11 Fir siding. (no this foam is not a second vapor barrier). In side I used poly VB, OSB and paint.

If you insulate the perimeter WELL down below the frost line then your ground temp under the slab will be roughly ground water temp ~ 54 degrees. I keep my 2 story 28' x 48' at 63 - 65 24/7 during the heat season which comes out to ~$150.00 a year with NG FA. Floor is about 2 degrees lower than inside air temp in the Winter months.
Summer temp goes to a high of 73 -74 w/o AC. I credit the 1" Dow foam inside and outside my foundation block down to frost line plus another 1" under the entire 5" cement floor for the comfort I enjoy. My build, in 1981, preceded Tyvek in my area or I would have used it. The T&G Dow rigid foam and Dow Corning Mastic 111 for all joints was the best I could do at the time.

 

[ADSR]

The foam on top of the sheeting makes a HUGE difference in controlling cold joint transfer. It boosts the effectiveness of the rest of the insulation in the building. It's now code here for multiplexes.

 

[c6matt]

Thanks for the info Sands...that looks perfect

Steve, you have me wising I had insulated the floor/foundation before I poured it.. hopefully that's the last "wish I had" on this project...

Lord Diesel, what thickness is code?

 

[sands35]

You can go down the outside of the foundation wall. The foam will need to be capped or just run up the entire wall. At and a bit below grade, you will want to install something to protect the foam from mechanical damage (i.e, weed-whackers). I used aluminum flashing.

My garage's foundation and slab was done in 1 pour. I still have 2" xps under the slab though. I put 3" of EPS against the outside of the foundation. Covered with flashing.

 

[volleyball]

Hi density foam will be the vapor/wind barrier so that is all you need, no tyvek needed.
If you do the ceiling, you don't use baffles, the foam goes directly on the deck and cover the trusses too.
If you go with batts in the wall, and foam on the outside, sealing the joints will negate the tyvek. Long nails can be ordered. Locate the framework before you put on the foam boards so that you will know where to nail.
You can also remove the fill against the building and put in foam boards vertically down to the footing. This will help big time with heat loss and frost heaving under your slab. Cover the foam with something to protect it from damage.

 

[c6matt]

You can go down the outside of the foundation wall. The foam will need to be capped or just run up the entire wall. At and a bit below grade, you will want to install something to protect the foam from mechanical damage (i.e, weed-whackers). I used aluminum flashing.

My garage's foundation and slab was done in 1 pour. I still have 2" xps under the slab though. I put 3" of EPS against the outside of the foundation. Covered with flashing.

what would you do for my exposed corner? any pics of your garage with the lower flashing?

 

[volleyball]

PT T11 or stucco would work. Would it be viable to backfill that space? Maybe a short retaining wall.

 

[c6matt]

Hi density foam will be the vapor/wind barrier so that is all you need, no tyvek needed.
If you do the ceiling, you don't use baffles, the foam goes directly on the deck and cover the trusses too.

The foam would not go on the roof sheeting, it would go on the metal "flat" ceiling of the garage, with the attic uninsulated. Does that change your advice on the Baffles?

The builder was contracted to frame/sheet and shingle with the walls wrapped in tyvek, the money on that is already "spent" does it hurt to have both?

 

[volleyball]

The baffles would only go where the roof meets the wall if you don't have raised trusses and you have soffit vents.
With a metal roof, if you can lose an inch, putting sheets of foam between the metal and the framing will go a long way towards maximizing your envelope. Plus the thermal break helps keep the upper side of the metal from rusting.

 

[Kevin C]

http://www.foamular.com/assets/0/144/172/174/e45fe07d-5cc9-4e4b-866a-5e35d75090ec.pdf

http://www.buildingscience.com/doctypes/enclosures-that-work/etw-high-r-value-enclosure-assemblie

http://www.buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriers?topic=resources/vapor_barrier_code_changes

http://www.buildingscience.com/documents/bareports/ba-1301-guidance-taped-sheathing-drainage-planes

A few good links.

Foam on the outside wall (foam with foil) will require most drying to happen to the inside.

There is a ratio of inner insulation to outer foam to make sure that the condensation point is somewhere in the foam, and not in the wall. To make this work, the more insulation in the studs you have, the more foam you need outside.

No matter what you do, I would recommend a drain plane.

 

[c6matt]

Hi density foam will be the vapor/wind barrier so that is all you need, no tyvek needed.
If you do the ceiling, you don't use baffles, the foam goes directly on the deck and cover the trusses too.
If you go with batts in the wall, and foam on the outside, sealing the joints will negate the tyvek. Long nails can be ordered. Locate the framework before you put on the foam boards so that you will know where to nail.
You can also remove the fill against the building and put in foam boards vertically down to the footing. This will help big time with heat loss and frost heaving under your slab. Cover the foam with something to protect it from damage.

http://www.foamular.com/assets/0/144/172/174/e45fe07d-5cc9-4e4b-866a-5e35d75090ec.pdf

http://www.buildingscience.com/doctypes/enclosures-that-work/etw-high-r-value-enclosure-assemblie

http://www.buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriers?topic=resources/vapor_barrier_code_changes

http://www.buildingscience.com/documents/bareports/ba-1301-guidance-taped-sheathing-drainage-planes

A few good links.

Foam on the outside wall (foam with foil) will require most drying to happen to the inside.

There is a ratio of inner insulation to outer foam to make sure that the condensation point is somewhere in the foam, and not in the wall. To make this work, the more insulation in the studs you have, the more foam you need outside.

No matter what you do, I would recommend a drain plane.

looking at this from your link, the tyvek is the drain plane correct?

 

[ADSR]

Lord Diesel, what thickness is code?

When i went to look at how they did it, they used 1 1/2 blue. And it doesn't even get real cold here in victoria. Another thing they had to do was, they added a piece of 3/4 plywood to the bottom of the rough window opening flush with the front of the foam. This is so the window is supported by wood and not sitting on the foam. You'll have a wider window liner on the inside. Remember, everything will need to be packed out.

 

[volleyball]

There are so many variables that the thing about the drain plane could be right or wrong.
Foam is not foam. When it comes to performance, there are big differences.

 

[Steve in Mi]

what would you do for my exposed corner? any pics of your garage with the lower flashing?

I used brown Aluminum flashing that went up 1.5" behind my Fir T1-11 siding and down 10.5" which got m well below the ground fill level.

Your exposed corner will be more challenging. May 3' or 4' wide flashing to treat that corner area and narrower material for the rest. Some have used a stucco to cover the exposed foam.

 

[jack stand]

On your exposed corner (pic), you could hold your wall OUT 1 1/2" on your plate, then "furr out" the masonry with 2x2's to allow space for foam down to or below grade then attach the finish or siding to these strips. Insulation is good! Money well spent.

 

[c6matt]

On your exposed corner (pic), you could hold your wall OUT 1 1/2" on your plate, then "furr out" the masonry with 2x2's to allow space for foam down to or below grade then attach the finish or siding to these strips. Insulation is good! Money well spent.

thats a good Idea, do you mean to build the wall of the garage out over the foundation to allow it to flow seamlessly with the foundation wall?

 

[WVBrady]

looking at this from your link, the tyvek is the drain plane correct?

I am curious about the answer to this question. It appears that there is a drainage space (shown in brown) that is separate from the building paper or house wrap, but it doesn't explain how it is obtained.

 

[sands35]

The whole idea with putting foam on the wall (as far as water and vapor management) is to get the dew point inside the foam (1st choice), and to pick the correct vapor barrier on the inside face of the wall the control moisture. This will ensure no condensation on the interior of the wall and to limit condensation when conditions will create it - and avoid nastiness like black mold or dry rot.

The wall system needs to be matched to the HVAC system. (i.e., some combinations require a slightly higher interior air pressure to control air flow through the wall.)

There will be some months in the winter when the dew point is not inside the foam. The assumption is that the inside face of the wall is semi-permeable AND you have some sort of humidity control to dry out the wall.

Engineering data:
http://www.buildingscience.com/documents/guides-and-manuals/gm-guide-insulating-sheathing

Assuming that we are talking about garages with the assumption that the HVAC system isn't fully conditioned like it would be in a house, a lot of the engineering is out the window.

I've been around and around the raw engineering calculations on this. I eventually came back to just doing it the way that houses and garage have been built for 50 years. i.e, siding, house wrap, OSB, studs, kraft faced insulation, drywall and paint. Just make sure to detail away any air leaks.

I think that a lot of folks that only use part of the whole system are setting themselves up for problems. (i.e., only using foam and not an HVAC with HRV for example). There are a lot of homes that where built early in the super insulation kick that now have rotten walls.

Basically:
Keep liquid water out
Allow the wall to breath enough to dry it out when water does condense.
Avoid air leaks

If I lived in a colder area I might add some lath 90* off the studs to limit thermal bridges. If it was really cold, I'd use a 2x6 wall.

Going nuts on insulation and missing something critical like the HVAC system will just create more problems than you solve.

The basic problem is that all the heat load and insulation calculators assume an interior temp of 70*F. But most folks seam to run their garage at 50*F in the winter - at least I do. I'm doing hot work anyway (sanding, planing, hucking tires / transmissions / etc. around.)

 

[c6matt]

So I dont want to mees up the HVAC portion, I was planning on doing a vented radiant tube... anything to watch for? And I will be keeping the garage cool in the winter. 45-50...

What is HRV?

 

[volleyball]

Hot Rod Vehicle!!!

may be Heat Recovery Ventilator.

 

[sands35]

haha - yes, heat recovery ventilator.

I've seen a few threads where somebody spray foams the whole garage, then wonders why there is condensation dripping off the inside.

The newer insulation systems work great. But heavy emphasis on "system". All the parts need to be put together to make it work.

 

[jack stand]

The whole idea with putting foam on the wall (as far as water and vapor management) is to get the dew point inside the foam (1st choice)

Good post!!

thats a good Idea, do you mean to build the wall of the garage out over the foundation to allow it to flow seamlessly with the foundation wall?

Exactly!

 

[jmlcolorado]

I am a construction manager for a large home builder and all of our homes are energy start rated.
The construction is 2x6 insulated walls, txvek exteriors taped at every seam, "quick flash" boots over every single penetration, gasket end electrical boxs which are then foamed behind with fire foam. All framing is then foamed where the bottom plate meets the foundation and at all corners. Drywall has a gasket that staples to the top and bottom plate. Attic access all have latches and weather stripping (like you see on a front door). Vapor barrier installed inside under the rock (your requirements. I tht differ depending on what climate your in).
Our homes are so air right we are required to have a whole house fan (80 Cfm exhaust fan) running at all times in the laundry rooms. Exhaust only. There is no intake.
Hot water heater and furnase are both sealed high efficiency so no open air to the house.

This system is efficient and quite affective. I would reccomended this to anyone looking for air sealing.
The garage doors, however, have nothing different than the standard weather sella, though they are r12 insulated.
Hope this helps.

 

[WVBrady]

I am curious about the answer to this question. It appears that there is a drainage space (shown in brown) that is separate from the building paper or house wrap, but it doesn't explain how it is obtained.

This reference that was quoted appears to answer my question:

Engineering data:
http://www.buildingscience.com/docum...ting-sheathing

Edit: Sorry, this link doesn't seem to work. Use the one from #27.

It just shows the drainage plane as the house wrap. However, it also states:
"For Wall Section 1 and Wall Section 2, cladding systems such as traditional hard coat stucco (including thin brick and manufactured stone veneer) and acrylic stucco can be directly applied to the insulation board. With these types of systems it is recommended to use drained insulation boards (ones with vertical grooves cut in the back) or to use a vertically textured (or profiled) housewrap, to ensure that there is a drainage space behind the rigid board.