Underfloor insulation

This is the job that pretty much finished me off earlier this year. Looking back, I find that I started writing a blog post about this back in February, but that was before the trip to Cornwall with Dad...

Here's what I wrote in February:

This is the job that's been getting me down for the last few months. It feels like a bigger job than replacing all the floors in the house and come to think of it, it probably is. It's the same area (actually slightly more, because we didn't replace the sitting room floor but it still needs insulating), there are three layers to install, and all the work is overhead. But I'm getting ahead of myself...

Underfloor heating, viewed from under the floor

The pipes carrying hot water to heat our house run through the underside of the flooring panels and, where they need connecting together, are completely exposed below the floor. They needed to be accessible for installation so, once complete, our underfloor heating was heating the space under the floor. In this case this was the garage, workshop and store room, or a space equal to the house above.

When I was at school, we learnt about three ways that heat can get from one place to another; convection (heat rises), conduction (heat travels along some materials, such as metals), and radiation (heat will just float off into empty space if there's a hot thing surrounded by coldness). More recently, I've learnt that in the context of heating a house, convection is the one that does most of the work and radiation is pretty much irrelevant. Hmm, judging by how warm our unheated downstairs rooms are, I'd say that radiation can be quite important in a house.

So... insulation is required. In fact, insulation is part of the specification for the underfloor heating. If I'd noticed that earlier, I wouldn't have spent so much time trying to find out how much insulation I needed, as the answer was there in the spec. It's all very confusing, as sometimes it's expressed in terms of how much heat is let through, and sometimes in terms of resistance to heat (U values and R values respectively. At least, I think it's that way round. They're reciprocal, anyway.) If you're looking at layers of insulation, one kind - I think it's R values - can be added up but the other kind can't.

Once I'd found out how much I needed, I still had the problem of choosing what kind. This was difficult because rockwool is the work of the devil, but lovely fluffy eco-friendly stuff tends to be very expensive. I also wanted advice on what works well, so perused the Green Building Forum, where someone mentioned leaving an air gap between two layers of foil. That seemed like a good idea, especially as I already had one of the foil layers pasted to the underside of the heating panels. There's a modern type of insulation that consists of layers of foil and spacing, which is claimed by manufacturers to be equivalent to much thicker bulk insulation. The difference is that foil works as a reflective barrier, bouncing radiated heat back, whereas traditional insulation just traps as much air as possible without letting it circulate. If I could get the thinnest (cheapest) type of this fancy new foil stuff, that would make a good start to my insulation.

I wasn't particularly short of space, so no need to go for all super-thin fancy stuff. I'd fill out the rest with traditional bulky insulation. I'd much rather have nice eco stuff but, as noted above, it does tend to be expensive. I needed to know just how much more expensive, so set about doing a bit of research. I took the first price I found for rockwool, which probably wasn't the cheapest, as a baseline. Sure enough, most of the eco products I found were several times the price, until I came across Black Mountain sheep's wool insulation which was only 20% more expensive. I had to double check that, but it was true. It's also Welsh, so a relatively local product.

The only drawback of using sheep's wool (or indeed rockwool) to insulate a ceiling is that it's floppy, which makes it a bit of a challenge to put up. The third component of my insulation would have to be boards to hold the wool up. At this point I ran out of green-ness. I did check eco alternatives to plasterboard, but they were so expensive that I gave up and ordered standard, cheap plasterboard. At least it's not as nasty as rockwool to work with. I also bought sticky tape to hold the foil up and screws to hold the plasterboard up. As for holding the wool up, I'll come to that later.

Insulation in the garage, just waiting to be put up.

As you can see, the sheep's wool is indeed bulky, whereas the foil - just one roll, over there on the right of the photo - takes up far less space. I'm not sure if the plasterboard had been delivered by this time, but if it had, it's on that heap of boards in the middle.

So, I had all the stuff, I was ready to go... but a bit daunted by the task. It didn't help that the rooms I needed to insulate looked like this:

Garage, mostly full of insulation

Store room, mostly full of sundry crap

Workshop, mostly full of, well, more sundry crap

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So I'd written about the theory and planning, and some introductory stuff, but not got onto the actual work of putting up the insulation. I shall resume:

I started in the garage because most of what was in there was the insulation itself, and that heap of boards in the middle of the room made quite a handy platform to stand on when working on the ceiling. Also, the joists were parallel and evenly spaced in there, which made the job somewhat easier.

The first step was the foil-and-bubblewrap* layer. I found that if I cut it along its length, it had enough rigidity to hold its own weight when wedged between two joists, so the sticky tape didn't have much work to do. I still added it, to minimise air flow around that layer. Here's a ceiling with the foil layer in place:

Foil insulation taped to the ceiling - not the garage ceiling, but they all looked much the same.

The foil looks wonky in that photo because it had to go over (that is, under) some pipes. Once the foil was up, the floppy sheep's wool layer was next. My cunning plan for holding this up for long enough to get the plasterboard fixed underneath it involved wedging struts between the joists under the insulation.

Sheep's wool insulation

The struts in the photo above include foil tape (not ideal, relying on stickiness), buddleia sticks (from hacking back overgrown plants), and strips of Range Rover headlining (don't ask). We also used plastic conduit that once covered electric wires, polystyrene packaging, offcuts of pipes, and various other things that normal people would have long since thrown away.

Once the wool was up, we then moved on to the really difficult part (and sheep's wool, by the way, whilst much nicer than rockwool, still drops bits into your eyes when you're holding it over your head, and I'm still picking strands of it out of one wooly jumper I foolishly wore to work on this back in February). We bought plasterboard in 8' x 4' sheets. This is quite big. Certainly too big for one person to hold up while screwing it to the joists, and a bit much for two people, at least if those two people are me and Ian.

Taking advice from several people, including my dad, if I remember rightly, we tried assembling a jig consisting of one floorboard placed across the middle of the plasterboard to spread the weight and another jammed between floor and ceiling to hold it up. This was moderately successful, but did have a bad habit of collapsing dramatically as the board was screwed up, taking its weight off the support. Halfway through plasterboarding the garage, our very kind neighbours offered to help us, and the next bit was much easier, with four of us working together.

Garage, insulated and boarded

Leaving the garage behind, much moving of things was required to gain access to the workshop ceiling. This ceiling is conveniently divided into three sections by hefty beams running across the room, so I cleared just one section at a time, putting up all three layers in that section before moving things again to get to the next section. Again with help from our neighbours, and from another friend (who may have been bribed with cake), we managed to get the workshop finished.

Workshop ceiling. We weren't too fussy about the finish

I then moved everything from the store room into the workshop (making the workshop almost inaccessible in the process) and started work on the store room ceiling. I'd got the foil layer done and some of the sheep's wool at the point Dad needed my help with his house in Cornwall, so I left in the middle of the job, intending to finish it when I got back. On my return, utterly exhausted, I found that the wool had fallen down.

That was the final straw. I simply couldn't face it any more. And so the job was left, insulation variously hanging from the ceiling or sitting on the ground**, for several months. It didn't improve my motivation when I discovered that the wool on the ground had got damp and mouldy.

Back in March I assumed that I would recover from the Cornwall trip and get back to this job fairly quickly, but as I've discussed before, it didn't happen like that. Summer, such as it was, came and went, and the insulation still wasn't finished (and the stuff was going mouldy). My sister, kindly but firmly, told me to get a grip. Well, she didn't quite put it like that. She saw that this particular unfinished project was really getting to me, and something had to be done to get it moving again. "Just pay someone to do it," she said. She had a point (she usually does). It had got to the stage where I couldn't bear to even think about it, never mind face up to actually doing the work.

I asked Ian to take over responsibility for making something happen and agreed that it would be worth spending some money. He went round to see someone who does odd jobs for the hotel and had said to us at some point that if we needed stuff doing we should ask him. Within a few hours, he'd come round and the three of us were putting up insulation and plasterboard. Just like that.

There was a break for a couple of weeks as either he or Ian were busy doing other things, but then we saw him at the village lighting of the Christmas tree event last Sunday and arranged for him to come over again today, and now the job is finished. I won't say it was easy, but with someone else taking the attitude, "This is just a job to be done - let's get on and do it," the whole thing was a lot less daunting and, well, we did it. I am exhausted now, and my arms ache almost too much to type, but I am so pleased this is finished. I feel released from something that was dragging me back.

As a final bonus, when I asked, "How much do we owe you for all this work?" he said, "Nothing. I'll take payment in kind sometime when I need help with something." Isn't that lovely?

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* That's what this fancy new insulation looks like - a layer of bubblewrap sandwiched between two layers of foil, then coated with another thin layer of plastic to protect the foil. Makes sense to me.

** I use that word deliberately. There's no floor, as such, in the store room. In fact, parts of it are quite muddy.