Pamments / underfloor htg...ideal construction?

[Pford75]

We have a pamment floor, with the pamments laid directly onto earth. We are considering lifting the pamments to install wet underfloor heating as well as some insulation etc.

What would the ideal construction be? Base, insulation, any treatment for the pamments? Any recommendations or advice on the u/floor heating?

 

[AMc]

We excavated quite a way, top to bottom the construction is...

2" pamments laid on lime mortar
65mm concrete screed encasing wet underfloor heating
dpm
100mm of ecotherm insulation,
dpm
100mm gen 4 oversite concrete
25mm of sand
150mm of hardcore compacted

There is insulation at the edge of the UFH screed, doing it again I would have put in 25mm of ecotherm.

If you want/need a breathable construction you'll need to use LECA and limecrete.

You need to be careful about undermining the foundations so a test pit or two will be needed - our foundations are massively deeper than they needed to be. This also generates a hell of a lot of spoil which needs to be removed in several skips.

Our pamments were treated with Osmo Polyx which works well at repelling stains.

The underfloor heating is fed by a heat pump so it runs at a maximum of 55C which is also used by the radiators unmixed. If you have oil or gas heating you may need a mixer valve to lower the flow temp to the underfloor to prevent it overheating your feet or the floor.

Ours was installed by Eco Conversions from Blofield Heath in Norfolk - they're now part of Renenergy but are run by the same people and the same installation staff
http://www.renenergy.co.uk/underfloor-heating.aspx
Many plumbers are also now offering underfloor heating as it isn't particularly complicated - however it's very important to size the amount of pipe and pump properly so I would recommend an expert specifies the system even if you DIY or a plumber installs it.

 

[Pford75]

Thanks a lot for the info...very helpful. Anyone else have any info on Limcrete or LECA? We would need a breathable floor.

Did you use reclaimed or new pamments? We have a mix of sizes and some broken ones...would like to source reclaimed at a reasonable cost.

 

[Penners]

This is nothing more than amateur conjecture, but I would tend to avoid putting leca-based concrete/limecrete over the top of the UFH pipes (you'd probably already thought of that). Given its insulation properties, you could tend to reduce the upward heat permeation into the floor. But leca underneath would seem an ideal material, as it would add to the insulation that you will undoubtedly be putting in anyway.

 

[MdB]

http://www.limecrete.org.uk/about_limecrete_floors.html

 

[AMc]

This is nothing more than amateur conjecture, but I would tend to avoid putting leca-based concrete/limecrete over the top of the UFH pipes (you'd probably already thought of that). Given its insulation properties, you could tend to reduce the upward heat permeation into the floor. But leca underneath would seem an ideal material, as it would add to the insulation that you will undoubtedly be putting in anyway.

FWIW the concrete oversite under my insulation had aggregate, the screed that contains the the pipes was mixed sharp sand and cement pumped in.
I presume a lime screed for pipes would be sand and lime without any aggregate too.

I'm still slightly unsure how much moisture a couple of feet of limecrete/LECA and then a couple of inches of fairly impermeable, diamond hard pamments will actually 'breathe' but I'm in no way suggesting you shouldn't follow that route. As we have a glass structure and non breathing ecotherm insulated walls it was academic. As the sub soil was bone dry to the depth for hardcore I'm reasonably happy to take the risk but everyone's house is different.

Regarding pamments I was lucky that I had an original floor of 9"x9"x2" and some 12"x12"x2" that were able to be picked up, pressure washed and put back down - I ended up about 20 short thanks to cuts and some previous concreting in around the edges. I picked those up from a reclamation yard in Oak Street in Norwich for £2 each on a Friday afternoon when we'd run out but would have struggled to find a floor there and you had to sort through the piles yourself looking for ones exactly the right size without damage. They were selling ones in worse condition than ones we'd rejected as unlayable. One of the 9x9 we picked up looked salmon (like the floor) but turned fire engine red when we pressurewashed it!.

Bear in mind with reclaimed materials ones from the same yard, on the same pamment may turn out to be subtly different sizes and thicknesses. If you're intending to lay them close to each other without a significant grout line as per a traditional pamment on lime floor then they must be identical or you won't manage it.

We had a mix of yellow and red floor bricks that I planned on laying in the kitchen but they weren't the same size and couldn't be intermixed.
I made the mistake of making the red floor bricks go further by hiring a masonary bench saw and cutting them in half. Unfortunately the builders used a jig and the depths weren't even so we lost quite a few in cutting, more in laying and (because of the pillock who layed them) a lot in breakage since when they've popped off the mortar bed, rock and move against each other. It would have been infinitely preferable to have spent time sourcing enough to do the whole floor at full thickness.

I got some good leads on reclaimed roof tiles from http://www.salvo.co.uk/ in the end I used a guy called Neil Wilson who has/had yards in Kings Lynn and Thetford. He had a good supply of 9x9 when I got the tiles but it wasn't worth the trip/delivery when I needed only 20 in a hurry.
http://www.salvo.co.uk/forsale.html?key=pamment

You could also consider going new http://www.pamments.co.uk/ which would ensure you got a good even batch and wouldn't be significantly different in cost an would save a lot of trawling around.

 

[Penners]

I'm still slightly unsure how much moisture a couple of feet of limecrete/LECA and then a couple of inches of fairly impermeable, diamond hard pamments will actually 'breathe'

I think that's probably a fair point.. However, whether or not the oversite underneath the insulation is made with lime or OPC, I still think that using leca aggregate is good idea.