Retrofitting UFH and new ground slab

[Adman101]

I am looking to extend and retrofit UFH to my 1830s cottage. The two rooms which form part of the existing house are the hall and the dining room. The hall is within the original part of the house and the dining room was bolted on in the 90's. My concern is what construction to use in the hall. There is a small amount of damp in one corner around the fireplace, but the rest is damp free. If I didn't have any advice, I'd look to excavate it all, type 1, sand blinding, DPM, insulation and screed and UFH. The DPM would need to be tied in the existing stone work (400mm thick walls) by cutting a 1m slot and installing DPC and grouting back up. (for the exterior wall only). Is there a better way of undertaking such a task? Having read a few other posts, a few recommended a suspended timber floor but the posts were aimed at ridding damp issues, plus I'm not sure I like a timber floor construction with quarry tiles above.

I am unsure of the present floor construction and won't find out until I come to undertake it.

Also, will UFH be an issue with solid stone walls? Is it worth insulating the wall on the inside with insulated plasterboard? Space isn't an issue.

 

[mointainwalker]

In this respect there is no difference between stone walls and any other wall - what you want to avoid is direct connection so that your heated floor doesn't transfer some of its heat to the exterior.

The commercially available option that I see ( I live in France so may be different in UK ) is an adhesive-backed foam band which is approx 8 mm thick and 100 mm tall. I thought this was needlessly expensive as well as inadequate for insulation purposes and therefore simply cut up panels of 50 mm polystyrene insulation to create a break between the wall and the floor.

 

[theprinceofdarkness]

The reason for the foam around a concrete slab is to take up the expansion when you heat it with your UFH, else the slab which will grow when it is hot will push the walls out. It will reduce cold bridging as well. In theory it should be as thick as the underfloor insulation (4"?), but that will leave the edge of the floor around the screed unsupported. Top the screed with chipboard? Ya pays ya money. . . .
Frank

 

[mointainwalker]

In most cases the wall will also be insulated which would cover/take care of the "unsupported" bit, but even if that isn't the case, I find that the 100 mm around the periphery of the room gets surprisingly little foot-traffic