I recently bought a house in Houston that has a detached, unfinished three car garage. I want to sheetrock the garage interior and I’m thinking about insulating the garage while I’m at it. If I add insulation, will I need to add one or more windows to promote ventilation? I might add a window unit air conditioner this summer but I wouldn’t want to run it all the time.
I’m new to Houston and I don’t know if insulating the garage like this will restrict the ventilation in the garage and cause any problems due to humidity.
Assuming I do this, what’s the best way to insulate the “attic”? If possible, I’d like to use that space for storage so I don’t want to just blow in insluation. Can I tack insulation to the underside of the roof’s plywood deck?
Related to this, how can I determine the load bearing capacity of the rafters in my detached garage? The previous owner installed attic stairs and has 1/2″ plywood decking in place but I’ve heard (from a builder) that the garage rafters generally aren’t meant to bear significant additional loads beyond the garage itself.
Sorry for the long rant. Thanks in advance for your advice.
Phil
Replies
Greetings Phil,
This post, in response to your question, will bump the thread through the 'recent discussion' listing again.
Perhaps it will catch someone's attention that can help you with advice.
Cheers
If by ventalation you are talking about moving air for creature comfort then DW and insulation won't have any affect.
But if you want cross ventalation for people comfort then some windows will help.
In a detached garage you won't have humidity from people breahting, bathing, cooking, and a large number of house plants.
But if this was air conditioned continously you might have some problem with condensation from air the outside moist air that works through the walls.
But for short time AC I don't think that you would have a problem. Now i am not real familar with your climate, but I supsect that for this application either unfaced FG or blown in celulse would work.
Now insulation is only affective when the space is conditioned. In unconditioned space it only affects how long it takes for the space to reach ambiant tempature. But if you want to condition it part time I would go ahead and do it.
But in your climate installing a radiant barrier on the underside of the roof can really help with the heat.
The capacity of the attic floor joist depends on the size and spacing.
How far do they span?. What is the spacing?, What is the size.
If it is I-joist look on them for brand, size, and series markings.
Also it might be trusses. A basic gable roof will be a triangle made up of the ceiling joist and 2 roof joist. A truss will have other members connected together with metal plates.
I'm interested in using AC part time for creature comfort (me!) when I'm working in there. I just didn't know if installing insulation like that would cause moisture retention problems when the AC is not on in the garage. If I understand what you're saying, it won't.The garage is a stick built garage. I don't think trusses were used in the roof construction based on your description. I've attached some pictures to give you a better idea. I apologize in advance for not resizing them!AS far as dmiensions go:Three car garage - 20' x 30'
The joists are 2 x 1- (1.5 x 9?) 24" apart
The joists are 20' feet long
As I said, the roof is not constructed using trusses.If I install a radiant barrier on the underside of the roof, what specific product would you recommend?Thank you; Phil
20' single span 2x10's @ 24" oc won't support much permanent storage at all.... best i could find was 30 lb load for 16' span..
most lumber species ( the grade stamp on the side of each joist will tell the species & grade ) are in the 13' span range
as to your insulation question... you are in either a hot-humid climate zone.... ( i'd guess)
or possibly a hot-dry/mixed - dry climate
you need to develop a strategy so you don't wind up with moisture condensing inside your insulated wallMike Smith Rhode Island : Design / Build / Repair / Restore
I think Houston fits the hot/humid category. Two questions then.What strategy should I use? Do I need windows if I insulate that space? Second question is how do I increase the load bearing ability of the ceiling?Phil
google on Building Science Corp.. they have a strategy for hot-humid.. we area cold climate so a lot of my strategies would be the opposite of yours
to increase the load capacity of your floor system to any significance you would cut the spans in half or in 1/3 - 2/3 by installing a support beam
or.... since your joists are 24" OC... you could approach a 30lb. load by installing a joist between each joist so you wind up with joists 12" OC
go out to the garage & read the grade stamp on the joists so we can look up the rating for your lumberMike Smith Rhode Island : Design / Build / Repair / Restore
Mike,You beat me to it.Chuck Slive, work, build, ...better with wood
On the joists, the only stamp I see looks like this: S-P-F 46 S Dry
No. 3There's something that might be only a logo. Its above the number 46 shown above. It looks like a stylized "MF1"Is that what you need?Thanks again to all you guys.Phil
S-P-F means the species is Spruce-Pine-Fir ( all the same as far as teh strength tables go
and it's Number 3....( as opposed to number 1 or # 2 )
the allowable span for 30 lb. live load ( first floors are normallly designed for 40 # ) with a 20# dead load is 9' - 11"...
if you reduce the spacing to 12" oc
and your new joists are better grade, you will approach the 30#
best bet is to halve your span by adding a center post & beam
Mike Smith Rhode Island : Design / Build / Repair / Restore
I would go with two colums supporting a properly sized glulam beam or properly sized lvl with a flitch plate. 3-2x12's would also work because the span is just under 10'.You will have to sawcut the slab and put in footers. Turn the footers 45' to the outside walls.Chuck Slive, work, build, ...better with wood
I'm looking for recommendations on the best garage door company in Houston. I've been experiencing some issues with my garage door lately, and I want to get it fixed by a reliable and trustworthy company. I've done some research online, but I'm overwhelmed by the number of options out there.
Downside, you buried your question in a 20 year old thread.
Might try a social media venue in your area.
Nextdoor or even close area Facebook.
Or a local hardware store or lumberyard or a neighbor.
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