Garage insulation

[Jensmith]

I'm hoping to be able to insulate the garage which is slowly turning into my workshop rather than a general store room!

It's attached to the house so is brick built with 2 internal walls - attaches to the hallway and then the kitchen runs along the back of the house so the garage is accessed through the kitchen.

The roof is a proper felt roof - a flat roof, with beams internally and chipboard boarding so you could put insulation between the beams.

It's a concrete floor and has fiberglass garage doors. We were thinking of making a false wall across the garage door end as the best way of insulating and cutting down draughts.

i've seen various posts on insulation but scanning through none seem to be for a garage or workshop that's attached to the house with a proper roof so I'm guessing the methods might be different if it's not a corregated roof etc.

What insulation type would you recommend and do you need to leave a gap for airflow if it's a standard felt roof?

Is there anything else you would recommend in terms of insulation?

Thanks,

Jennifer,

 

[Nicknoxx]

I'd use 50mm Celotex or Kingspan. If you look for seconds you can find it for £10/sheet
I'd leave it flush with the face of the 'beams' so there's a gap behind it, but that might not provide adequate ventilation. If you have a vapour barrier on the hot side of the insulation you can prevent warm moist air cooling and condensing on the timbers.
A stud wall across the fibreglass doors is a good idea but make sure you can still get big stuff in and out.
Ideally insulate the floor by laying 2x2s with insulation in between and ply on top. Again you might need a vapour barrier so use foil backed insulation and tape the seams.
uk.d-i-y has loads of advice on this subject.
Nick

 

[Carlow52]

The felt roof is a problem as both the felt and the chip are water vapor impermeable and therefore if you insulate from below the effect will be to bring the dew point further into the roof space and you will get condensation on the beams and the chip.

The theory is that if you put a vapour barrier on the hot side of the insulation the problem is eliminated.
Even if you do this layer to a very high standard and have no perforations for cables lights etc the problem that will arise in the summer is that the roof-space will heat up and convert some of the current moisture in the chip and beams into water vapour in the roof space which will then condense as water.

IMO you need to think about ventilating the roof space to the outside and then insulate away to your hearts content.

The run of the beams vis a vis the 2 internal walls will determine how hard it will be to ventilate

If you have a water vapour problem with the existing roof it will last 5 to 10 years

For the floor I would get a good pair of hiking boots or work boots with steel toe caps and good socks

For insulation I prefer the type of stuff here http://www.ecologicalbuildingsystems.com/?country=gbr as opposed to the rigid poly_X's

For the external wall could you consider external insulation?

I dont need answers here, just posing questions as a basis for ideas :deer

In passing, how old is the felt, does it need replacing?
Could you contemplate replacing the felt and adding some insulation from the outside while doing so