U-value of Ground Floor

Longford Leader

Hi, could somebody explain why the max u-value of a concrete ground floor with u.f.h, is lower than the max u-value of a concrete ground floor without u.f.h. in the current building regs.

sydthebeat

The lower the u value the better.

The minimum u value for a floor with UFH in the upcoming regs is 0.16, where as other floors are 0.2

0.16 is 20% better than 0.2

sinnerboy

0.15

sydthebeat

my bad!

smooth operater

and of course its assumed the insulation is going to be placed under the pipes......

smooth operater

smooth operater wrote: »

and of course its assumed the insulation is going to be placed under the pipes......

Do you know of someone who put it over the pipes? :eek:

ircoha

After much discussion with a client who has a HP/UHF set up and the HP was being blamed for not doing the business, I convinced him to allow me dig up a bit of the floor in the utility room..

The 'PU' insulation was there okay but it seems to have 'crumbled' away.
As I 'dont do' UHF, I got an opinion from someone who does.

His view was that the concrete had eaten away the foil and the PU was 'corroded' by the concrete.

He says that there has to be plastic between foil backed and concrete.

His current installation method is plastic sheeting over the foil backed pu, with taped 300mm overlapping joints.

He then supports a393 mesh on the plastic and ties the UHF pipes to it.

He argues that the mesh set up is better than the clips that pierce the membrane and that sometimes lift out during the pour, particularly if the concrete is 'lashed in'.

As to what my client does next: sin sceil eile as the builder is gone bust.

sculptor

What is happening with PU and concrete in walls ?

Do-more

ircoha wrote: »

As to what my client does next: sin sceil eile as the builder is gone bust.

Has the insulation manufacturer expressed a view on this?

What are the manufacturer's installation instructions for this type of installation, if they don't include a plastic barrier between insulation and concrete I'd be going after them for supplying a product not fit for it's intended use.

Mellor

Syd and sinner are correct that the u-value limit is lower for UFH, but that doesn't answer the OPs question

Longford Leader wrote: »

Hi, could somebody explain why the max u-value of a concrete ground floor with u.f.h, is lower than the max u-value of a concrete ground floor without u.f.h. in the current building regs.

He wants to know why it is that way.
Its quite simple, a U-value is a measurement of how heat passes through a body. It is made of of W/mK
W is the energy per second
M is area/thickness
K is delta Kelvin (which is exactly the same as delta celcius)

If any of these increase of decrease the heat loss is change proportionally.

With radiators heating the room the concrete floor is at a temp of maybe 20 degrees (inner surface)
With UFH is might be about 40 degrees, so the heat passing into the external ground is higher, the insulation is increased to compensate

sydthebeat

Mellor wrote: »

With UFH is might be about 40 degrees, so the heat passing into the external ground is higher, the insulation is increased to compensate

as an addendum to that...

because UFH works at lower temps than a rad system (typicall 40deg vrs 70 deg) any extra heat loss is proportionally larger for UFH so its easier to make it inefficient and ineffective due to inefficient insulation.

for example, typically 60mm PU insulation will meet minimum 0.2 u value, where as 110-120mm PU insulation will be needed to meet 0.15 u value.