Garage ceiling insulation

danoriordan1402

Looking for some tips on how to insulate a block garage ceiling. There is an attic area above that is used for storage etc and its just boarded out with OSB. The external walls were done during the initial build with pumped beaded insulation. The main area below is now going to be used as home office space. Any ideas on what would be the most economical way to complete it, its about 25sqm.

I am wondering do I need to maintain an airgap below the OSB flooring above and install some kind of vapor barrier.? The plan will be to have some kind of heating in the main space. If I do need the airgap then would that mean i'd have to make a gap in those small timber pieces inbetween the joists ?

whizbang

If you have enough height, just use rigid board fixed to underside. You dont need any extra air gaps.

Otherwise pack fibre between joists, and slab over.

Or both!

10-10-20

Well-fitted glasswool and plasterboard would probably be acceptable here as long as the storage area above is ventilated. The concern though would be that moisture penetrates the plasterboard and condenses on the underside of the OSB, especially around any penetrations such as downlights. Foil-backed plasterboard would keep this in check as long as the room below isn't heavily moisture laden.

GreeBo

What are you going to be doing in the garage?

Insulating it sounds like you are going to be living/working/working-out in it which will change the thermal properties of the building.

Whats above the OSB? Is the roof line above insulated for example?

Boarding the joists is going to cut all airflow so if you are going to be introducing moisture then you might create a condensation issue.

GreeBo

Are the eaves of the attic root ventilated at the moment?

Basically you are turning a cold space into a warm space so you need to control any moisture (which you didnt before)

If the walls are insulated I would have expected the attic to either be warm already otherwise I'm not sure of the point!

Would need to know more detail about where the joists meet the walls and what ventilation is there at the moment.

Depending on ceiling height you could board underneath and drill 25mm holes through the joists to increase airflow, or cross batton and board to that. But none of that achieves anything unless there is already airflow between the joists from outside.

danoriordan1402

https://www.boards.ie/discussion/comment/120879554#Comment_120879554

The attic space is usually sweltering during the warm summer days and bearable during the winter ;) Adding some more pics below for context. Attic space over is not insulated but does have roof vents in the slates, currently used for storage overflow. The OSB wasn't nealtly cut out for the floor around the joists just thrown down as you can see.

GreeBo

Its hard to be 100% sure from the pics, but it looks like you can maintain through ventilation by just cutting some holes in the noggins and boarding directly over with rigid boards, tape the seams and then fit plaster board/osb/ply as desired (or do nothing!)

It appears that you will maintain airflow from the eaves between the joists from side to side and also up into the attic space. You should tape your seams and tape the insulation to the walls.