Garage interior boarding out

[Steve Senior]

Hello group members,

I'm new to DIY and have set myself the task of renovating the interior of my outside garage. I figure I can make my mistakes in there whilst using it to learn what I'm doing as I go along.

What I'm trying to do is to batten the walls and roof, insulate and board out all over effectively making it into a regular "room". I've not thought about the floor yet. One end will have gym equipment and at the other end I intend to have workbench and storage.

I've never done anything like this and have so many questions rattling around my head but wanted some general advice on how to approach this in stages, and which stage to do first etc. I had thought I would find this on YouTube as I can't be the first to do this, but I've searched as best I can and can't find any videos going end to end.

The plan in my head is this:

1. Batten the walls and roof ready for boarding
2. Insulate walls and roof
3. Board out with something (do you use plasterboard in a garage?)

A couple of pictures to show you what I am working with:

I'm at a bit of a loss as to how to attach anything to the roof as it has metal beams and it seems like it could be asbestos sheets.

I'd just to like to get the conversation going about how to start here.

Thanks in advance, Steve

[The Natural Philosopher]

First comment to make is that the roof will be the greatest heatloss. That you can simply wedge celotex/kingspan in between the rafters, foil up for airgap elimination and or use expanding foam,. and plasterboard over.

On the walls 3 or 4" battens with the same insulation and foil BUT if you want a load bearing wall for shelves etc then consider using MDF. I used that in my main kitchen and it proved fantastic at taking pint and at hanging cupboards off.

Obviously run any wires and pipes before plating over the walls.

Windows don't look too bad but that up and over door may prove a lossy and draughty component

[Fredxx]

<snip>

Why foil up? The corrugated nature of the roof will ensure some ventilation above the celotex.

[Theo]

Before you do any of that, look at 'warm roofs' and 'cold roofs'. London Flat Roofing on Youtube has a good series:

The key is that, unless properly ventilated, an insulated roof will rot (in this case rust). Condensation forms inside the structure and can't escape.

A warm roof is one where you put the insulation above the roof so the structure is snug and 'warm'. A cold roof is where you put it below - the critical part here is that the timbers or metalwork has ventilation so any moisture can escape.

I guess you have two choices: build a sub-ceiling below the existing steel with an ventilation gap between it and the steel, vented to the outside - this is a cold roof.

Or replace the asbestos with some kind of insulated deck. For example, you might find that an insulated panel would be an easy swap for the asbestos sheet:

The downsides of doing that are the extra height (possible planning implications) and whether the steel structure will take the extra weight (may have to upgrade - eg with timber). OTOH it will likely look smarter from the outside once done.

The other thing you'll learn from London Flat Roofing is the importance of detailing: you can slap on insulation, but unless you do the joins correctly (eg wall to ceiling) you either get heat loss or moisture problems.

Theo

[The Natural Philosopher]

Its ventilation *below* the celotex one is trying to eliminate, dear.

[The Natural Philosopher]

I thought I saw corrugated cement board? Plenty of ventilation

It will be a cold roof of necessity as the cladding is corrugated

Make up your mind whether it's corrugated iron, cement board or asbestos...

For example, you

[Theo]

It appears to have a steel frame. If doing a cold roof you need all the steelwork in the ventilated space, otherwise the parts of steel that poke through the insulation will have potential for trapping moisture, and that's where they're likely to rust.

I never said anything about corrugated iron. Looks like (asbestos) cement board on a steel frame to me.

Theo

[Jeff Layman]

That depends.

When we moved in the garage had been partially converted to a dog-grooming salon. The roof (which we soon replaced, was originally corrugated, but was probably not asbestos thank goodness) was insulated by 2" expanded polystyrene, and covered with hardboard screwed to the battens. The walls were done similarly. Everything was fine until something buggered up the fluorescent lighting wiring and it kept tripping the MCB and RCD. It was simply not possible to remove all the hardboard and insulation to examine the wiring behind to find the fault. I just disconnected it and bypassed it by fitting new wiring in trunking over the hardboard.

[Fredxx]

A membrane stops water vapour condensing. A wet piece of Celotex where warm, moist air has condensed in the foam is going to be less effective. Hence the mass of Celotex needs to be kept at dry as possible, with the membrane on the warmer, moist side.

The Celotex should be fitted such there is minimal ventilation from below the Celotex to above it.

[The Natural Philosopher]

No, that's the point of sealing with expanding foam. |Or Foil. either the steel is inside the insulation, where it can get warm dry to stop condensation, or it is outside and ventilated or it is covered in foam otr foil and so has no access to atmospheric oxygen

Well you burbled on about rust. Cement boards (can't be any asbestos LEFT post the Great Asbestors Panic) don't rust. That steel RSJ skeleton could rust for 50 years without becoming structurally weakened !

[The Natural Philosopher]

Well that is a perfectly sane approach. The cost benefit to debugging/fixing old shit or simply bypassing it with new is something every heart surgeon understands :-) BUT unless you have mice, PVC coated cable in walls wont go wrong.

If you DO have mice, well, all bet's are off..

As good a bit of earth leakage as you are likely to find.

Its the second 'critter induced trip' I've had.

Another one got into the loft and chewed through a bit of lighting wiring, years ago.

That's another good reason to seal up the room very well indeed

[The Natural Philosopher]

Have you ever used celotex? Its not a bathroom sponge, you know. It doesnt *get* wet.

At the very worst it allows a slow permeation of gas through it, which foil stops

That's the point of sealing the gaps with the foil tape dear.

And or foam if the tape gets tricky.

>

[Fredxx]

This has some useful tips.

[Fredxx]

Rather this does:

[Steve Senior]

Thank you for all the replies.

Focussing on the roof for now, this may be a silly question but assuming I get the insulation done correctly and wedged in between the steel trusses, how would I get the plasterboard fixed in. I can't fix to the steel as I see it, am I supposed to put wooden battens either side of the steel trusses then fix to that? If so how do you batten wood onto steel?

[John Rumm]

Greetings

Sounds like a good plan :-)

I have done very similar on my workshop - masonry walls and traditional trussed roof with slate over.

I wanted insulation with a ply lining (ply being much easier to fix stuff to later, which is handy in a workshop).

I did not bother with battens are all, and just placed 50mm foil faces PIR foam[1] insulation against the wall, taped all the joints with foil tape, and then screwed the ply straight to the masonry using long (5") screws into plugs in holes drilled through into the masonry.

The PIR boards are very strong in compression, so you don't need to worry about the ply or fixings covering them.

[1] Polyisocyanurate foam is a fairly dense foam with very high insulating properties, and is often bought with a foil covering adhered to one or both sides to act as a vapour barrier. Common brands incluse Kingspan, Celotex, Ecotherm etc.

For the roof I would build a false ceiling below - it can be pitched to match what is there or flat. So 2x2" timber around the top of the walls, and then infill with 2x2" on a 600mm spacing. The beams would only need run mostly in one direction but with noggings every so often where the board ends are likely to fall. Again you could insulate this with PIR boards below and ply or plasterboard under, screwed through both into the timber.

(you can also get plasterboard with the insulation and the vapour barrier stuck to it ready to go straight up).

This would create what is called a "cold deck"[2] roof, so all the warm wet air is contained in the room so that it can't get to the roof structure, and that just has natural ventilation to the outside (which you tend to get by default with a corrugated roof panel).

[2]

Best to leave it alone with a "new" ceiling a inch or two below.

This explains why it is important to control vapour when adding insulation:

[jim.gm4dhj]

bloody DIyers

[Fredxx]

I would prefer plywood rather than plasterboard, as per John's suggestion. I would have thought some hook bolts would be a means to attach the plywood to the metal rood trusses.

[Tricky Dicky]

Looking at your photos you have a wallplate on the brickwork, you could create rafters that met at the apex and at the base attached to the wallplate that would give you space to push your insulation in between and also provide something to fix boarding to. You may have to provide some additional fixing of the wallplate to the brickwork there are various galvanised straps that could be used.

When I created my Mancave in the back end of my timber-framed garage I simply cut PIR boards to fill the bays between the studs and the roof trusses. Foam was used to fill any gaps this is important to prevent localised cold bridging and then to create a continuous vapour barrier all joins and studs etc were foil taped as in the link John provided. Finally everything was boarded with PB.

One thing I would suggest is to surface mount your electrics, flush fittings will require digging out cavities in the insulation which then becomes a PITA to restore the vapour barrier. Mine was all done in trunking and conduit and a dado trunking.

Richard

[Jeff Layman]

Was it easy to find? Or did that wiring block have a cover over it?

I doubt it'll be the last.

It's almost impossible to seal up a loft or garage from the teeth of those little pests, as they've got such flexible bodies and can get through the smallest hole. I know we've got them in the loft and the cables to the garage run from the loft. Unfortunately, they seem to be getting wise to the mousetraps baited with peanut butter. :-(