I'm thinking about ripping up my floors and making them airtight and insulating them using this system - https://www.ecologicalbuildingsystems.com/Ireland/Blog/Post-Detail/A-Best-Practice-Approach-to-Insulating-Suspended-Timber-Floors

While I've got everything up I was thinking about installing some UFH. I understand the aluminium heat spreader plates are quite good. However my joists seem to be at between 320 and 360mm between centers. The narrowest spreader plates I can find are 390mm. I don't really fancy cutting them down to size with tin snips.

So is there somewhere you can get narrow spreader plates or is there anywhere that hires out metal type guillotines? Or is there some better alternative?

Thanks

Well actually there are two rooms I am going to do.
One I will put back the original floor boards as that room is carpeted.
The other room I'll put down some sort of hardwood, whatever I can find cheap at the time!

I'm not sold on a particular spreader plate yet, though I am wondering if this might do the trick - https://underfloorparts.co.uk/product/ffb-fit-from-underfloor-heating-ffb-double-spreader-plate-spreader-plates/

It is meant to go under neath but I figure I could straddle each joist with one of these and that would pretty much get my spacing right with no cutting. I think it will have less contact area and I am not sure if will have enough pressure on the floor above to make a good contact. From what I have seen on videos the spreader plates are all a bit flimsy and don't look like they make great contact anyway. Do they actually work??

Last thing, I'm concerned about (which I just realised) is where do I put the air tight membrane? Above or below the UFH? I am thinking below, but I will need to give it some slack and also notch all the joists before installing it so I can get the pipes though.

Phew, not sure I still want to do UFH!

Thanks Will that is really interesting.

I don't like the sound of all the creaking from the spreader plates. I also don't have the height to lay fermacell or similar over the top.

Are there any other good between joist solutions?

>>Are there any other good between joist solutions?

Have you looked into https://www.google.com/search?q=ufh+biscuit+mix

No personal experience, but sure others here have..

I did a bit more investigation on the weekend. Looks like my joists are only 100mm!
I'm hoping there are a few extra bearers there but I couldn't check that with the limited access I currently have.

So I'm thinking the extra load of the biscuit mix might not be ideal, also wouldn't leave much room between the joist for insulation.

Also thinking it might not be ideal to notch what little joists there are. Instead I thinking these boards might be best - https://www.renewableproductswarehouse.com/timberjoisted-floor-heating-systems/35-lk-slotted-board-wood-22.html
I will loose a bit of height but I think I can live with that.

Anyone have experience with those?

Posted By: derekeI will loose a bit of height but I think I can live with that.

Why will you lose height? they should replace the floorboards.

Though I don't share the opinion that spreader plates are good (I'm not so impressed, having fitted them In a couple of different floor build ups) but I can promise that they're thin and easy to manipulate. You won't need to cut them; if you need then narrower just place them against a sharp edge (length of square edge hardwood screwed to a bench will be fine) and run the heel of your hand along it to put a crease in it, then fold them over onto themselves like closing a book, then open them out again with the fold jammed into a sawn slot of depth that is half the distance you want to narrow them by. They will thus have an extra rib down the middle that is eg 30mm high and the whole plate will be eg 60mm narrower

I was given a load of 2 groove plates but they didn't suit my desired pipe spacings; the grooves were 200 mm apart and I needed 125, so I made a jig (a bit of wood 15mm thick, screwed to a bench) up to flatten one of the grooves and a press (sounds fancy, it was just 3 bits of 6x2 with a 15mm copper pipe screwed to one face and a 16mm groove in the desk. I could flatten and re-press two new grooves into a plate in about 90 seconds. For the fourth groove (I needed there-back-there-back between each joist) I cut spreader plates in half by scoring then with an angle grinder and snapping them, though I expect a Stanley knife would work just as well. In summary; you'll be able to fold and shape them at will with just your hands, scissors etc. You definitely won't need an industrial guillotine

All in, if I were doing it over, I would have battened out the joists 80mm down from the top, dropped a 50mm slice of kingspan on top of the battens and clipped the pipes to it, then laid - rough sand /cement screed.. but the plates were a gift so it was the cheapest way to go. They're also quite easy to fit to the underside of an existing floor, even though multiple UFH installers said they wouldn't/couldn't fit to underneath existing floor boards and were insistent on an overlay system or ripping up; the 22mm eggerdeck came as part of the timber frame and I wasn't keen on the idea of paying for another floor deck nor removing the glued-n-screwed one I already had :)

If you're laying the pipe yourself I'd definitely recommend a pipe with an aluminium core. Non alu core pipe has a life of its own whereas the cores stud stays however you bend it and is much easier to fit (imho)