Underfloor Heating

[NWhit]

Hello,

I am thinking of adding wet underfloor heating to the ground floor of my house. I know there needs to be breathable insulation in old homes does anyone know if this can be done with underfloor heating?

Thanks

 

[lookseehear]

Hi - this is a very useful link, particularly section 4 where it discusses materials https://historicengland.org.uk/imag...ing-solid-ground-floors/heag087-solid-floors/

 

[Glenn586]

Hello,

I used 300mm of foam glass with a 150mm limecrete slab on top. Topped off with 75mm thick yorkstone's I am the proud owner of a gigantic radiator. It works a treat.

Good luck

 

[aockenden]

Hello,

I am thinking of adding wet underfloor heating to the ground floor of my house. I know there needs to be breathable insulation in old homes does anyone know if this can be done with underfloor heating?

Thanks

Yes, you can safely insulate an old home's solid ground-floor (while maintaining breathability of the floor) to the point where underfloor heating becomes feasible (from a downwards heat-loss point of view). The solution to this combination of conditions is usually referred to as a "limecrete" flooring system. The procedure involves digging-up the existing solid ground floor, excavating quite of bit of subsoil, then laying down a thick layer of a chunky insulating aggregate such as foamed-glass or LECA (lightweight expanded clay aggregate). Then you basically layer over the top of that with an NHL lime screed (NHL 3.5 or NHL 5 for floor strength). Then you lay your finishing tiles (often breathable limestone tiles) onto that NHL screed (bedding and grouting with more NHL). That's a broad overview, there are a few pieces such as breathable geotextile fabrics involved which I didn't mention.

 

[Kearn]

The general consensus as NHL continues to be understood (and continues to harden) is that the slab is pretty irrelevant in a limecrete floor system. Concrete is being used instead, as some NHLs set harder, eventually … the important part of the floor system is the glapor (recycled foamed glass) - this acts as both insulator and capillary moisture break, so the depth of this is important. As is the cork expansion and thermal perimeter of the slab. You don’t wish to be heating the subsoil! General view is that the limectete slab doesn’t really breath, nor does it need to. Therefore stressing over breathable final floor covering is probably a waste of time, to be fair even limestone slabs mostly moisture manage through their pointing gaps.

But wet UFH works very well if done correctly. Perfect low and slow way to keep old fabric warm.

 

[Stevers]

Ties in with concrete slabs in conventional construction requiring a DPM!

 

[Toby Newell]

The general consensus as NHL continues to be understood (and continues to harden) is that the slab is pretty irrelevant in a limecrete floor system. Concrete is being used instead, as some NHLs set harder, eventually … the important part of the floor system is the glapor (recycled foamed glass) - this acts as both insulator and capillary moisture break, so the depth of this is important. As is the cork expansion and thermal perimeter of the slab. You don’t wish to be heating the subsoil! General view is that the limectete slab doesn’t really breath, nor does it need to. Therefore stressing over breathable final floor covering is probably a waste of time, to be fair even limestone slabs mostly moisture manage through their pointing gaps.

But wet UFH works very well if done correctly. Perfect low and slow way to keep old fabric warm.

++ Exactly this. Complexity doesn't sell and thus vendors bang on about the lime part of limecrete as most potential customers already know about the breathability of lime plasters.

In reality the limecrete is pretty irrelevant, in a well executed install the RFG provides a breathable, free draining, non wicking barrier between the subsoil and the self insulating slab (which is mixed with more RFG or expanded clay aggregate) So, you have less moisture below the slab (and thus walls) to be wicked upwards, retarded wicking of any residual moisture and less condensation through the insulating effect.

The limecrete is somewhat breathable and this does help, but in a good install it is only really wicking moisture from the adjacent 100mm depth of wall and distributing it accross the slab. Effectively the limecrete slab is acting as a moisture reservoir that can slowly dissipate that reducing the moisture load on the adjacent walls.

The system should really be called Insulated-glass-crete but limecrete sounds sexier and is easier to understand.

The idea is fantastic and is used widely now in industry in large commercial projects, but with Portland cement concrete due to limes poor strength. They still get 90% of the benefits of a free draining, insulating, breathable dpm.

 

[Toby Newell]

^^^ thus, if you have a severe rising damp problem and / or the space is below ground level the limecrete slab part would still prove beneficial and so would having the gold standard top floor, which would be sandstone over UFH.

For milder rising damp situations a normal concrete slab might still do enough with just the draining and insulative effects.

 

[Flyfisher]

Hello,

I used 300mm of foam glass with a 150mm limecrete slab on top. Topped off with 75mm thick yorkstone's I am the proud owner of a gigantic radiator. It works a treat.

Good luck

Me too. I had a large floor consisting of pamments laid directly on earth. A previous owner had laid a softwood floor over the top but this was badly decayed as a result of the constant damp through the floor. After the wood flooring was removed the floor was fine except in any area that was covered and therefore unable to breathe to disperse the damp - something we soon discovered after moving in an storing cardboard moving boxes on the floor. Within a few months the base of the boxes were damp and falling to bits!

We lifted all the pamments and installed a wet UFH system based on the foamed glass design described here: https://www.mikewye.co.uk/product/glasscrete-floor/ and rebedded the pamments on the limecrete slab. We no longer have the damp problem, even when the UFH is not in use, which I assume is because of the size of the foamed glass beads not supporting capilliary action through the floor.

All in all, a good solution for period properties with solid floors and no DPCs. Obtaining LBC was not a problem either.