Insulating and heating question.

[FRS FAN]

Hey Guys,

I have a 21x21 Garage, with 2x4 construction. I dont know much about insulation but I was told R12 is the highest R-value of insulation I can put in my 2x4 walls.... Is this true? If so would it be worth it to do Double Drywall for extra insulation or would you add 2x2's to the 2x4's to be able to install R20 bats? -- (btw I plan to put R20 or R40 insulation for the ceiling).

Next question is I'm planning to run a direct vent wall mount natural gas heater... does anyone know how far the vent has to be from a fence (combustibles) because my fence is only about 1.5 meters from the side of my garage where I want to vent out.

So my plan is R12 walls, R40 ceiling and a 15,000 BTU Natural Gas Heater..... for my 21x21 garage (400Square feet)..... any advice?
Thanks!

 

[pattenp]

Double layer of drywall isn't going to provide any added insulation benefit. You could do a layer of rigid foam board. The 3.5 inch fiber glass batt insulation should be R-13.

 

[p_mori7]

I have a 21x21 Garage, with 2x4 construction. I dont know much about insulation but I was told R12 is the highest R-value of insulation I can put in my 2x4 walls.... Is this true? If so would it be worth it to do Double Drywall for extra insulation or would you add 2x2's to the 2x4's to be able to install R20 bats? -- (btw I plan to put R20 or R40 insulation for the ceiling).

Next question is I'm planning to run a direct vent wall mount natural gas heater... does anyone know how far the vent has to be from a fence (combustibles) because my fence is only about 1.5 meters from the side of my garage where I want to vent out.

Thanks!

R13 is the actual rating for the fiberglass bats that fit into a 2x4 stud cavity.

Install a vapor barrier afterwards.

Install 1x3 strapping at 16" or 24" intervals perpendicular to the studs to create an air space (acts as insulation). You could also add some 3/4" foam board in between the strapping.

Install your drywall onto the 1x3 strapping.

 

[Kevin C]

For a premium, you can get R15 fiber glass for 2 x 4 walls. After installing the fiberglass, you can also put foam directly over the studs and then put the sheet rock directly over the foam. You will need longer drywall screws.

I used XPS foam. The advantage of foam is it gives you a very good thermal break. It's possible to use 2" R10 foam and end up with a very well insulated wall. The trick seems to be sourcing 4" drywall screws.

View media item 32288
http://www.fastenersuperstore.com/partNumber/263731/CPG/Screws/10-X-4-Drywall-Screws-Coarse-Phillips-Bugle-Head-Steel-Black-Phos

Or use strapping to make your wall cavities deep enough for 5 1/2" thick insulation. Each layer of drywall adds about R.5 ( not a lot).

Any air gap from about 1/2" to 4" adds about R 1.

 

[FRS FAN]

Hmm, Thanks alot so far guys. I think I will get the Roxul R15 for the walls and the Owens Corning R40 for the attic area.

I just found out my Garage door is only rated at R8... I read quite a few reveiws that the R-rating of the door doesnt matter as much as compared to how well it is sealed. This is new construction and the R8 door is what the builder has provided.

Do you guys think adding one of those garage door insulation kits will be sufficient... its the reflective kind that adheres to the back of the door... they are also Rated R8... I presume this will give me an R16 garage door??

 

[jameswood]

Kinda funny for a Gdoor with a good R rating only to leave the sides and top with just that std plastic door seal. I double insulate mine using the vinyl covered foam door insulation (like used on entry doors and fits in slot at door edge) on inside and makes a big improvement on air infiltration.

 

[trainer]

r-13 will be sufficient for the walls. Just make certain you do a good job, good vapour barrier and tape all the seams with tuck tape. Put the extra effort and money into into more attic insulation and make sure your doors and windows are well sealed.

Consider blown-in attic insulation, it's fast and easy to install with a rental blower, and make certain you have proper attic ventilation.

 

[jameswood]

For a premium, you can get R15 fiber glass for 2 x 4 walls. After installing the fiberglass, you can also put foam directly over the studs and then put the sheet rock directly over the foam. You will need longer drywall screws.

I used XPS foam. The advantage of foam is it gives you a very good thermal break. It's possible to use 2" R10 foam and end up with a very well insulated wall. The trick seems to be sourcing 4" drywall screws.

View media item 32288
http://www.fastenersuperstore.com/partNumber/263731/CPG/Screws/10-X-4-Drywall-Screws-Coarse-Phillips-Bugle-Head-Steel-Black-Phos

Or use strapping to make your wall cavities deep enough for 5 1/2" thick insulation. Each layer of drywall adds about R.5 ( not a lot).

Any air gap from about 1/2" to 4" adds about R 1.

Awesome wall there Kevin and right (as usual) re thermal break! "thermal break" is too often ignored or not understood by the public and most builders in effort to cut costs.

I needed 9 inch screws and washers for my 6" EPS ceiling insul and could only find comm roofing screws and plates in 1000 qty which of coarse cost much more than planned! LOL long screws aint cheap!

 

[Kevin C]

r-13 will be sufficient for the walls. Just make certain you do a good job, good vapour barrier and tape all the seams with tuck tape. Put the extra effort and money into into more attic insulation and make sure your doors and windows are well sealed.

Consider blown-in attic insulation, it's fast and easy to install with a rental blower, and make certain you have proper attic ventilation.

R13 is probably OK... But since the OP is in Canada it might be worthwhile to use an online calculator to be sure.

http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm

This one seems reasonable.....

Wagging the building info....

On a -20°F day with R13 walls and an R40 ceiling I get about a 16,436 BTU per hour loss.

Ceiling Loss 992 BTU/HR
Wall Loss 6300 BTU/HR
Garage door 1800 BTU/HR ( I calculated the garage door as a 10' x 16', R8).
Floor Loss 0 BTU hr
Slab Loss 3780 BTU/hr
Infiltration 3564 BTU/hr


Cost to heat per year at 8000 degree days (US dollars):

If you heat year round ... Probably low since i guesses on your degree days, figure is for Butte Montanna) .
R13 walls ~ 5040 BTU/hr $425 year
R18 walls ~4200 BTU/hr $382 year
R23 walls ~ 3287 BTU/hr $358 year

R13 walls might be OK but could be limiting it you have a lot of cold days. If you heat the garage to 68 for the whole season, having R23 walls saves $67 per year. 2" Foam would cost you about $600. Disregarding the cost of money, it would take ten years to see a payback.

One question would be how often do you use the shop ( pay back on insulation) and where in Canada are you (lowest expected temperatures, and degree days).

 

[Gary S]

R13 is all you need in the walls. Heat rises, so walls lose very little heat with R13. You would never notice the difference between R13 and R19 in walls. You definitely want at least R40 in the ceiling because that is where the heat wants to go. If you have R13 walls and R40 ceiling, almost all your heat loss after that will be your windows and doors.

 

[trainer]

Hey Guys,


Next question is I'm planning to run a direct vent wall mount natural gas heater... does anyone know how far the vent has to be from a fence (combustibles) because my fence is only about 1.5 meters from the side of my garage where I want to vent out.

So my plan is R12 walls, R40 ceiling and a 15,000 BTU Natural Gas Heater..... for my 21x21 garage (400Square feet)..... any advice?
Thanks!

I have a direct vent NG heater too. 35,000 btu unit for a 28x28 garage. Mine is about a metre from a fence but you should to check with the manufacturer to be certain

 

[FRS FAN]

Thanks to everyone who has replied, very valuable information here. I almost feel like an expert now! (almost is the key word).

Anyway now I'm feeling like the Natural Gas heater I bought is going to be too small @ only 15,000BTU. It drops down to -5 farenheit here for a few weeks in the winter. I'd like to keep my garage at 45-50 Farenheit over the winter months. Not so sure 15k btu is going to do it. I got the heater used (less than a year old) for $200, so it seemed like a deal at first.

 

[Reg1952]

I used R13 in my walls and had R50 blown into the attic.My shop is 28 x30 with 4 windows One man door and 2 8x7 main doors.I think there R9.I live in Southern Ont. and my wife parks her car in there every night in the winter.I leave the t-stat at 50.I heat with a propane radiant heater and it only cost about $400 - 500 a year to heat.

 

[jvitez]

+1 on Roxul. I used it in my garage and I'll use it again when I build a detached garage. It allows a higher R-value per inch, and most importantly it REPELS water, very cool. So waaaay less mold risk. It's kind of fun to work with too, like cutting a pumpernickel loaf with a bread knife and sticking it in your walls.

 

[Kevin C]

Ceiling Loss 992 BTU/HR
Wall Loss 6300 BTU/HR
Garage door 1800 BTU/HR ( I calculated the garage door as a 10' x 16', R8).
Floor Loss 0 BTU hr
Slab Loss 3780 BTU/hr
Infiltration 3564 BTU/hr

BTW... Thanks James, sounds like you have a great setup!

One thing to note is that the majority of the heat loss is through the walls.

What is interesting is the ratio of R value that's recommended for the ceiling vs the walls. At R40, not a whole lot of ceiling losses, but the losses through the walls are 6 X higher.

The heat rises aspect is the typical explanation. However, the temperature gradient from floor to ceiling is usually less than 7°F. That is not enough of a temperature differential to justify R40 in the ceiling and only R13 in the walls.

The main issue is the walls have a lot of surface area. The other part is they are harder to insulate than the ceiling.

The third part is the temperature differential is a lot greater in the summer when the attic gets hot. IMHO that is the main reason to have a lot of ceiling insulation, I don't see the benefit in the winter.

Basically, the laws of heat transfer are not suspended because its a wall, its all about Delta T and surface area. In the winter the temperature differential on the walls and the ceiling is very close, it makes sense that the insulation values should have a similar ratio ( for winter calculations).

From a comfort stand point, warmer walls and ceiling reduce radiant losses from the body, that reduces how warm you need to make the room to feel comfortable ( more is better).

A easy to miss point is that putting R13 or R15 insulation in a wall does not get you an R13 or R15 wall. Thermal bridging across the studs, sill plate and headers will reduce the effective value to around R11 or so. That's why foam sheathing and construction methods that isolate the studs are popular.

My real point is to evaluate all the losses and see what makes sense. I plan on keeping my shop for a very long time so the investment made sense. I should be able to heat my shop on a cold day with an 11,000 BTU heater.

The final factor is air infiltration...

 

[FRS FAN]

BTW... Thanks James, sounds like you have a great setup!

One thing to note is that the majority of the heat loss is through the walls.

What is interesting is the ratio of R value that's recommended for the ceiling vs the walls. At R40, not a whole lot of ceiling losses, but the losses through the walls are 6 X higher.

The heat rises aspect is the typical explanation. However, the temperature gradient from floor to ceiling is usually less than 7°F. That is not enough of a temperature differential to justify R40 in the ceiling and only R13 in the walls.

The main issue is the walls have a lot of surface area. The other part is they are harder to insulate than the ceiling.

The third part is the temperature differential is a lot greater in the summer when the attic gets hot. IMHO that is the main reason to have a lot of ceiling insulation, I don't see the benefit in the winter.

Basically, the laws of heat transfer are not suspended because its a wall, its all about Delta T and surface area. In the winter the temperature differential on the walls and the ceiling is very close, it makes sense that the insulation values should have a similar ratio ( for winter calculations).

From a comfort stand point, warmer walls and ceiling reduce radiant losses from the body, that reduces how warm you need to make the room to feel comfortable ( more is better).

A easy to miss point is that putting R13 or R15 insulation in a wall does not get you an R13 or R15 wall. Thermal bridging across the studs, sill plate and headers will reduce the effective value to around R11 or so. That's why foam sheathing and construction methods that isolate the studs are popular.

My real point is to evaluate all the losses and see what makes sense. I plan on keeping my shop for a very long time so the investment made sense. I should be able to heat my shop on a cold day with an 11,000 BTU heater.

The final factor is air infiltration...

I'm hiring you to be my insulation consultant!