Garage Conversion - Insulation

Schorpio

Hi all,

Looking for some advice from knowledgeable folks about adding some insulation to an existing garage.

We're planning to convert part of our existing garage into a home office. We're lucky to have a large garage which is external to the main house. Plan is to leave some of the garage as-is, but partition off a room for an office. Garage currently has no insulation, just concrete floor and block walls.

Current thinking is to insulate the new room internally on all sides, but I'm slightly concerned about creating a damp environment.

For the floor I'm thinking I'll lay a damp proof membrane onto the concrete, followed by the insulation (PIR boards). Then lay chipboard on the top, covered by flooring to finish.

The walls are my main area of concern. I'm thinking of fixing studs to the block walls and insulating between. Then add a vapour barrier and finish with plasterboard.

I reckon this should be okay, but any input would be much appreciated!

Tweeter

The more insulation the better. You just need to warmboard the external walls and make sure you add some vents. The roof would be what I'd focus on first which you haven't mentioned. How is the roof constructed, flat, pitched?

Schorpio

Cheers - roof is pitched, but there is no ceiling, just the exposed rafters. I'm going to add a ceiling to the 'room' bit only and leave the rest as it. That way I can add insulation directly above.

When you say "warmboard the external walls" - do you mean do that externally or internally? Ideally I'm hoping to work internally only, as I'd rather only insulate the section I need, rather than the whole building.

Kaybaykwah

Have you thought out your heating source? You might take a look at radiant heating from your raised floor. My garage is heated that way, and is mostly used as my studio space. It has three zones where you might only need one?

It is much colder here than in Ireland, and it does the job.

Tweeter

https://www.boards.ie/discussion/comment/121366573#Comment_121366573

I meant internally. What you're describing yourself above, as in studs, insulation and plasterboard finish was the old way of dry walling. This method has been replaced by warmboards fixed on using insulation fixings or dabbed on using plasterboard adhesive. 62.5mm warmboard would do a good job or if you have the room available 102.5mm warmboard would be even better. If there is any windows, then you can use 26.5mm warmboard for the reveals

Schorpio

https://www.boards.ie/discussion/comment/121366967#Comment_121366967

Ahh, I didn't realise. Thanks for the info. I presume the vapour barrier then goes behind the warmboard?

Tweeter

https://www.boards.ie/discussion/comment/121367152#Comment_121367152

Not required, everything required is already on the warmboard. You just fix them directly onto the walls, make sure you have adequate vents and then skim or tape and joint to finish

bunderoon

Looking for some guidance on the same.

I want to convert garage to home office. House and garage built in late 1970s. Cavity wall with 70mm polystyrene insulation.

It will have a TV etc on south wall, desk with laptop with screens on north east corner and a wall mounted 2Kw (8.7A) radiator under the window. 2.5sqmm Tw+e on its own RCB back at main CU already. I cant see me using more than 12Amps so 2.5sqmm should be plenty for the room.

The floor, 4 walls and ceiling need insulating. Ceiling needs to come down a few inches to bring it to 8ft so thinking of cross battening 4 x 2s (16" on center) so it will be plenty of area to take 37mm plasterboard. Ceiling joists are 6x2 so would also either take rockwool or rigid insulation between them.

Garage is set back attached to the north facing gable wall of the house. New triple glazed sliding door and window. Sliding door faced west and window faces north. As the garage is stepped back, the north gable wall of the house puts this garage in the shade until late afternoon when the sun moves around to due west.

The garage was plastered when it was built so it has a smooth level surface to take PIR.

I am thinking of 80mm PIR straight to the wall and seal with metal tape (Vapor Barrier), then batten with 50mm x 50mm (long screws to secure batten and PIR to wall), then plaster board to the batten. This leaves me with a 50mm service cavity for power and data. I would think that if the budget would stretch, put 50mm PIR between the battens, again sealing with metal tape while leaving vertical space for the power conduits that would come down from the ceiling.

Run 6sq or 10sq SWA or Tw+E cable from house CU over across the attic and down to the right of the sliding door for future EV charger. Same for Cat6 for data and CT clamp.

The Sliding Door is sitting 6 inches above the concrete floor. Floor is a little sloped down as you go to the east wall to cant be bothered going with a floating floor. Will put down 1200g DPM and up the walls 300mm, then 5x2s (packed to level) which will be insulated between. Then 11mm OSB, then 12mm laminate flooring.

130mm total PIR may be a little too much and if so, I can go with 50mm PIR at the wall to bring overall depth to 100mm PIR. Conscious of the depth of the window and door reveals if going with 130mm.

I would greatly appreciate some advice here on the above whether its OK or if changes are needed.

Thanks.

bunderoon

@Tweeter @Kaybaykwah

Any thoughts on the above? Does it look OK to ye?

Kaybaykwah

I think you’ve done a good job preparing this project. Will you be laying down PIR on the floor before your laminate flooring? I am not sure if you said your floor is slightly raised or not because of incline and garage door.

If you had a bit of play, it might be worthwhile going the radiant heating for your floor. I did for my garage but it was a new build. All I can say is if you max your insulation the right way, it will pay off. I am not an expert but I live in Canada, where the weather goes from extreme cold to very warm/hot. So far, the bills have been reasonable because the insulation was maxxes out.

I would consult with other construction pros in Ireland to check on things. Even someone like the lumberyard guy in charge of providing materials to contractors would know quite a bit about this.

You did a great job with your plans and you will be happy when all is done. Good luck and keep me posted!