Underfloor heating coils buried too deep - is there a 'get out'?

[pandim]

[FONT=Arial, sans-serif]Complicated story. We are renovating the kitchen area of our 200 year old house built on a slight slope, putting in gas boiler hydronic underfloor heating. The floor at first seemed to have only one 4.5 inch (12 cm) step part way along its old uneven flagstoned surface. One of us has a history of falls and we are advised that a gentle ramp (1 in 12) is safest and this was designed for a short but narrow part one third way down the araea so that the sides of the ramp were not a hazard. Floor dug deeply down, one area 4.5 inches lower than the other, to lay insulation, subfloor, screed etc so burying the heating coils.[/FONT]


[FONT=Arial, sans-serif]Oops! The floor levels were not judged correctly. The lower part of the floor (about one third of total area) was found to be another 4.5 inches (12cm) lower than envisaged - viz needs another step or ramp. Lowering the whole floor is not practical because then becomes too low for drains and walls would need major underpinning etc. The already planned ramp is in a narrow part and extending it (to retain the 1 in 12 gradient) would intrude too much into the eating area, so another ramp, or a step, his has to go elsewhere. All accept this is best fitted at entrance to the kitchen area. It is suggested we simply cover this area with seasoned timber planks on 4x2 joists making it overall 4.5 inches higher.[/FONT]


[FONT=Arial, sans-serif]Differing opinions about this: (1) Surveyor says it will 'work' arguing that the underfloor heat has to go somewhere and as it is well insulated below and to the sides this can only go up through the boards, even if a bit more slowly than originally planned. Or (2) the heating installers say the wooden boards with the trapped air below will probably act as insulators (like double glazing) thus making the underfloor heating ineffective.[/FONT]

[FONT=Arial, sans-serif] Who is right? If (2), what other solution is suggested? Might abutting the boards deliberatly leaving slight gaps rather than tongue and groove fitting make any difference?[/FONT]

 

[Gray0689]

No 2 is right and it's a big problem that needs the manafacture of ghe underfloor heating your using to state what it needs doing to rectify

 

[Stephen@nic]

if you lay under floor heating on wood you get a over lay matting that will only push the heat up. it is for were people want to put underfloor on floodboards it takes up about 18 mm but i am sure that wont be a problem. dose this help

 

[unguided1]

I agree with gray on this the timber flooring will act as an insulator

 

[pandim]

Thanks Stephen. Perhaps i did not make it clear that the coils are presently buried at what I presume is the 'correct' depth in screed, a vinyl floor over it being propiosed - the latter not yet laid. Because of the error over levels it is now proposed to place timber on top of the screed to bring level up 4.5 inches. The coils would then be under the timber.

 

[pandim]

I agree with gray on this the timber flooring will act as an insulator

Thanks unguided1

 

[Stephen@nic]

best thing to do is go to the polly pipe \polly plum website and have a look at wot they have i know there is a over lay system they do with a heat profe mat that pushes the heat up and dose. i have fitted this for people and it works well. but yes they are write you can not lay it stright on to wood the wood will insolate it and itf the wood has more than 4% water content it will start to bow.

 

[Stephen@nic]

i just read wot you posted the wood will insolate yes but i would phone polly plum up they have a team for this type of prob they will tell you wot to do

 

[unguided1]

Who made the mistake when digging out the floor?

 

[pandim]

Who made the mistake when digging out the floor?

Good question! Not the heating installers who put it where they were told to.

 

[unguided1]

If the proper insulation been used underneath the underfloor pipes why not just put in a thicker screed I know this is not ideal, but it would work better than putting timber over the top with an air gap.

I dont suppose yer able to post some pics on here??

 

[Gray0689]

What I see is the only problem with a thicker screed is the heat up time for the thermal mass
But would at least work but if you put in the timber boards with an air gap it will not work
(just in case you don't know if you going to put a timber floor on top of underfloor heating you can't use solid timber it has to be engineered timber flooring also not all carpets and vinyles are compatable)

 

[pandim]

Thanks Gray, Assuming one can connect it up, would it be correct to say the "best" solution would be to disconnect the old coils and lay completely new ones on top of the present layer, burying these in new screed to the required higher level? I preseume that digging up to rescue the old coils would be very time consuming and more costly than simply adding a new layer of screed? From your comments the main disadvantage of the latter is a time delay in heat penetrating through?

What I see is the only problem with a thicker screed is the heat up time for the thermal mass
But would at least work but if you put in the timber boards with an air gap it will not work
(just in case you don't know if you going to put a timber floor on top of underfloor heating you can't use solid timber it has to be engineered timber flooring also not all carpets and vinyles are compatable)

 

[Gray0689]

Yes I would see a big delay in heating this thermal mass
You cant
Just add new underfloor on top of the screed or you will lose the heat into the lower screed you will need some form of insulation so the heat goes in to new screed
I have had to use a multi layered insulation before due to height restriction and then used a liquid screed (cemex) as this can be used a lot thinner than sand and cement
And is a lot better in my opinion for underfloor systems