Insulation Help

[fstilts]

Hi Guys,

I am new to this so if its a beginner questions sorry.

I live in Ontario Canada and winters get really cold to work in the Garage up here.

My question is: I have roof trusses in my garage that I use for storage but they are in W cross pattern so I can't really use it to make a loft. But I want to insulate without losing storage space. So I don't want to completely close it up.
Can I insulate right below the roof and leave the trusses open. Some one told me its not a good Idea because if I put insulation right up against the roof panel it will rot eventually. Is this true and is so does anyone know of something I can use or do?

Regard
fstilts

 

[Matti]

I think you would have to treat it like any other vaulted ceiling then. All the trussed areas would now become heated. I can see the concern for rot as there is no attic space to be ventilated now. I'm thinking that you need to put some kind of spacers in to create space between the insulation and the roof sheathing. I'm assuming that walls don't require this as they don't tend to be wet for long. If you research insulating vaulted ceilings perhaps you will find some ideas as to how this is looked after.

 

[thdewey]

I was just doing some research on this myself. I found this .pdf helpful:
http://www.southface.org/web/resources&services/publications/factsheets/25_insulateceilings_4pdf.pdf

 

[sparky1562]

Have you considered spray in foam? It is more expensive then fiberglass or blow in foam but can be sprayed to the underside of the roof. You want open cell for this not closed. (If you have a roof leak, open cell will pass the water and it will dry out, closed cell will trap it).

My house and it's attic is done with Icynene brand, and I just did my detached garage, which has both W trusses and Sisser trusses with Demilec, another competitor. I think by most codes, you would have to put a drywall ceiling in at the bottom of the trusses, but the truss 'floor' would now be a part of the heated space and still usable.

 

[Stuart in MN]

I think the biggest problem would be sealing around all the members of the trusses - it will be really hard close up all the air leaks. How about insulating the ceiling in a regular fashion, and then add a hatch you can open up to get into the attic space? By the way, those kinds of trusses aren't designed to hold any real amount of weight; putting some cardboard boxes full of Christmas ornaments up there is one thing, but if you're storing heavy auto parts it's not a good idea.

 

[GSSFC]

Have you considered spray in foam? It is more expensive then fiberglass or blow in foam but can be sprayed to the underside of the roof. You want open cell for this not closed. (If you have a roof leak, open cell will pass the water and it will dry out, closed cell will trap it).

Closed cell foam is a superior product in every category except price. If you have a leak, you have a leak, it shouldn't make any difference what you use for an insulation, they are mutually exclusive. If that open cell will "pass water" as you say, it will also allow air to pass through as well. That warm air that is able to pass through can also reach the cold roof deck and condense causing moisture problems. You still need a vapor barrier installed if you chose open cell.

Tim

 

[BooUrns!]

Look for some roof ventilation panels at HD. They're made of the same styro that egg cartons are made from and they get stapled to the underside of the roof. This gives you a ventialtion channel under the roof so you can place fibreglass batts against the ventilation channels. You'll need to keep them in place with some string lattice or mesh but it's the cheapest solution for what you want to acheive. This will give you your warm space without causing moisture problems/potential ice dams.

Icynene is a good product but is massively overpriced considering it is only 1/2 lb foam. If you were going to go that route, 2 lb. foam would be the (expensive) best product type to utilize. It's closed cell foam and has a much higher R value per inch. I see Icynene as an overpriced feel good product as it still only has an R value equivalent to fibreglass batts yet costs much more. They claim it acts as a vapour barrier but I've come across literature that speculates that the 1/2 lb foam may shrink over time allowing air leaks. 2lb foam doesn't do this.

 

[timgr]

There are 3 possible configurations for such roofs: hot roof, warm roof, and cold roof, and indicates the relative temperature of the underside of the sheathing. Each has a different way of dealing with the potential for condensation (and resulting rot) on the underside of the sheathing. The design usually called for by code and used in most construction in the USA is the cold roof, where the sheathing is ventilated by outside air, and this is what you see in the PDF provided above. A channel for cold outside air is maintained which is intended to remove any condensation by evaporation.

A hot roof places the insulation on top of the sheathing, keeping the underside at the interior temperature. The roofing is installed on top of the insulation. This is sometimes called an 'arctic roof' - apparently popular in extreme northern latitudes.

A warm roof places insulation in contact with the underside of the sheathing and uses a vapor barrier to prevent condensation. The vapor barrier must be sealed perfectly, otherwise air will infiltrate the insulation and moisture will condense on the sheathing. A sprayed-on closed-cell foam roof is an example. I have a warm roof in my little garage - fiberglass batts between the rafters and reflective bubblewrap as a vapor barrier. Sealing the vapor barrier around the garage structure took some doing, maybe three weekends of taping and gluing with silicone sealer. Not as easy as a cold roof, and could be problematic if you need to convince your inspector that it's acceptable. Works though - very effective.

 

[Druro]

Look for some roof ventilation panels at HD. They're made of the same styro that egg cartons are made from and they get stapled to the underside of the roof. This gives you a ventialtion channel under the roof so you can place fibreglass batts against the ventilation channels. You'll need to keep them in place with some string lattice or mesh but it's the cheapest solution for what you want to acheive. This will give you your warm space without causing moisture problems/potential ice dams.

I live in Mississauga, Ontario, and this is exactly what I did. In my case I had a "flat roof" but it does have a incline. I stapled the roof vents to the underside of the roof over the entire surface, and placed the bats against that. This leaves the air channel from the vented sofits to the "peak" of the roof.

 

[z28toz06]

if you go to this page:http://insulation.owenscorning.com/homeowners/ you will see a pink insulation foam -formed panel under the roof. This goes against the roof so the insulation does not hit it and get wet. The moisture travels up in a convective action and goes out the roof vent. If it precipittates or condenses and gets heavy it will run doen the panels and out the roof soffits.

I did my roof in 1/2 the house cathedral ceiling and used this so my attic would be insulated. It works well and have had no problems and nothing can freeze or overheat in the attic.

 

[bochnak]

I was just doing some research on this myself. I found this .pdf helpful:
http://www.southface.org/web/resources&services/publications/factsheets/25_insulateceilings_4pdf.pdf

Wow, it states that attic fans are NOT recommended. Guess I don't have to worry about mine since the motor is toast.

Sorry for the hi-jack...free bump

 

[sparky1562]

Closed cell foam is a superior product in every category except price. If you have a leak, you have a leak, it shouldn't make any difference what you use for an insulation, they are mutually exclusive. If that open cell will "pass water" as you say, it will also allow air to pass through as well. That warm air that is able to pass through can also reach the cold roof deck and condense causing moisture problems. You still need a vapor barrier installed if you chose open cell.

Tim

Not very accurate. The closed cell foam will trap the water. A vapor barrier is not required either. Talk to Icynene or Demilac. There is a proper place and use for each.