Garage roof insulation

fig1 - first load

 I've wanted to insulate my garage roof for ages.
Ideally I wanted to use 70-100mm Kingspan then foil insulate on top to help stabilise the temperature in the garage.
Unfortunately Kingspan is expensive and although I spend a disproportionate amount of time in the garage, I wasn't super keen to splash out on foam.

 Then a load of insulated barn walling came up for free down the road from me. This got me thinking out of the box and into my van. Two loads later and I had a lot of work sat in front of me.

The sizes were a bit all over the place as this was all scrap material but it was, for the most part 130mm thick and width was the same at a meter and a half.
By stripping off the inner and outer metal sheet, I was left with a corrugated foam board that could be cut to size with the only real issue being it was a bit deep.

Foam fit up

Ideally I would have flattened off each board then chiselled in each rafter and cross base so the foam would sit on top of and between each rafter running widthways. This would mean I would have around 4 boards per side, held in place by nails at each rafter. This would be tidy but would not allow for much roof movement and would be a bit of a pain to do.

fig2- One side foam instal done

Thus I cut each board so it would sit in between each pair of rafters like normal.
This required 3 measurements from each rafter pair (top, mid bottom) which I translated to the board to cut. This was needed as they were rarely parallel or even straight.
Once cut, I'd then trim off the ridges on the old ribbed outside of the foam and slot the board in. This worked 1/10 times, normally there was a bit of trimming required so I'd run a saw down the edge till I got a close fit. 
Each raft pair required 1.5 lengths cut, some stapled on duct tap helped things stay in place, then onto the next pair. I did have to add some small 5-15cm offcuts to the bottoms in some places to make up for variations in foam board width and my own cutting accuracy.

This process was repeated for the whole roof. Extra difficulty came in the form of the cross braises which I opted to remove then refit once all of the foam boards under it were in place. By drawing round the cross brace when loosely in place, I could then cut a channel into the foam using a Ryobi multi tool with a half mood saw for it to sit into so I got a fairly tidy finish.

This was very time consuming work. Not helped by the -5 temperature and having just contracted COVID. On the plus side it did give me the time to work. Thus after a week of solid snuffling and sawing later, I had done all of the foam fit.

Adding bubbles

So far this had only cost me some diesel and a fair chunk of time.

Next up I needed to at least tape, then cover what I had done.

After a few weeks I decided to take the plunge, purchasing 4 large rolls of foil backed insulation (I needed less than 1 for this job but plan to do the house next) and 5 cans (1.5 used)  of expanding foam, all on multi buy deals from Screwfix.

The foam was new to me so I wasted a bit putting too much in certain places. 

All that I had to do was spray all the areas I wanted to fill with some water then go crazy with the foam. Basically I just inverted the can and farted it into a gap till I had half filled the gap which was pretty close to right for most of the spots I filled. Some spillages were wiped up quickly, others were found later after hardening and chucked in a carrier bag full of offcuts for later.

The foil insulation was a fair bit quicker to throw up than the foam boards. I spent 3 days but it could have been done a fair bit quicker with less distractions.

I decided to go length ways across the rafters at the top as that was the fiddly bit, cutting round the verticals and ridge boards where they were doubled.
Next; I lay vertical lengths from the edge of the top section foil down to the fascia. Everything was stapled into the cross braces, facias and ridge where possible then edge taped with fibreglass reinforced tape.
In the middle section I had to dip into the rafters as there wasn't much to staple to. This made the middle a bit messy as there was a deep gap to get to the rafter between the over sized foam insulation, but this is a garage, not an art work so I wasn't too worried.

fig 3- one big and cozy tinfoil hat