Garage insulation spec: Suggestions\Thoughts

sas

Hi,

Currently considering how we're going to treat our garage. The sketch attached roughly describes the layout. Garage is 1.5 storeys. The intention is for most of it to be recreational (possibly Gym).

Basically we want everything upstairs (above red floor) and 1/3 downstairs to be warm (everything to the right of the blue partition). This area (to the right of the blue partition) is double height.

The garage was built with a standard 100mm cavity with no insulation in it.
The floor is treated as 1 large slab with 60mm PIR all around, including at the perimeter.
The roof has 30mm gutex on top of the rafters and 225mm depth of insulation possible below that.

What I was considering doing is as follows:

1. Insulate the middle floor with 225mm of mineral wool type material
2. Insulate the blue partition in the same (note: partition hasn't yet been constructed.
3. Insulate the roof with 225mm cellulose.

This is where the options arise:
(a) Constructing a 225mm TF structure inside the block inner leaf and insulating that.
(b) Use insulated plasterboard.

This would result in a pretty much cold bridge free structure (except at 1 door and window where the reveals were constructed the old fashioned way... and at the floor beneath the blue partition.

Would people favour (a) or (b) or an alternative such as pumping the cavity.
The reason I didn't consider that is because it wouldn't be enough insulation and also because the cavity was closed beneath the wall plate with a block so we'd have a BIG cold bridge the whole way around.

Thoughts?

BryanF

sas is this for your office or what is the expected use/ amount of time?
and what's the priority here? as in the insulated slabs are the cheapest (do the cavity first regardless)
I wonder would the 225 frame be too much insulation on the inside and cause condensation on your inner block face..

sas

BryanF wrote: »

sas is this for your office or what is the expected use/ amount of time?

Let's assume it may be a flat many years for now if a parent needed it. Planning and all that required of course.

Not planning on putting an office out there. If it's a gym it will be used at most a couple of hours every day.

BryanF wrote: »

and what's the priority here? as in the insulated slabs are the cheapest (do the cavity first regardless)
I wonder would the 225 frame be too much insulation on the inside and cause condensation on your inner block face..

This is what I was wondering about i.e. the doing the cavity regardless. I was also concerned about condensation on the block work as you've mentioned.

Bottom line is that this needs to be high spec cheap to heat space. It may not get done immediately depending on the budget (which is under pressure) but we'd rather do it right than fast.

Do-more

Can they do a blower door test on a garage door?

Only half in jest as there is no point in going for high levels of insulation if you are not going to pay reasonable attention to air tightness and in this case that will probably also mean between the heated and unheated spaces, what precautions are you going to take?

That of course then raises the question of ventilation, you don't want to smother yourself after a good workout! Some form of decentralised HRV with occupancy controls I would have thought. There is a crowd in Naas who could quote you, but I've no idea of price or I've seen Seamus mention a price of £1K for a FiWi unit....

What are you going to do for heating? In this part of a world a basic Panasonic air to air at under a grand would be the first choice but some form of fan assisted electric heater would probably do the job for reasonable cost, on a timer if you are a creature of habit or if not with a wireless control on the socket so you can switch it on half an hour before you are going to go out.