Floor & wall insulation calculations

derickmc

I am after received information from a builder on an old dwelling that I am assessing regarding additional insulation. I have a few queries as to how it should be considered for the BER

1)
The ground floor has been insulated with 150mm solid concrete slab insulated with 100mm of aeroboard.

My calculation for the thermal res istance would be 0.1 / 0.035 = 2.857
based on - thickness / conduct of EPS slab SD according to TGD L

There is no allowence for the concrete or wood flooring..
Just looking for confirmation on this.

2)
The walls have been drylined with Polyurethane board which has a conductivity of 0.021 according to the TGD L. Given that this work was under taken 6 years ago is this present day value valid ?

dunie001

The way you're doing it is right for the floor...just don't forget about adding the thermal resistance (TR) of the existing floor and the TR of the extra insulation together and work out the u-value from the total.

As far as the wall is concerned, you have to refer back to the TGD Part L that would have been in force at the time the work was done and use the conductivity given in it...in your case that would probably be 2002 Reg's

derickmc

Thanks dunie001, appreciate your help here.

dunie001 wrote: »

The way you're doing it is right for the floor...just don't forget about adding the thermal resistance (TR) of the existing floor and the TR of the extra insulation together and work out the u-value from the total.

Is this definitely the case? I was thinking that any old flooring would have been hacked up and replaced by the slabs. Mind you the property was built at the turn of the 1900's so the allowed insulation value is probably just accounting for the unfrozen ground below. That obviously still exists so you are probably spot on ..

dunie001 wrote: »

As far as the wall is concerned, you have to refer back to the TGD Part L that would have been in force at the time the work was done and use the conductivity given in it...in your case that would probably be 2002 Reg's

Nice one, I got the correct value in the 2002 regs.

Just a small thing.. I noticed in the 2008 regs is specifies Polyurethane board as being unfaced in the building materials section. This is not mentioned in the 2002 regs. However for correctness should 50mm Polyurethane board be considered. 37mm Polyurethane + 13mm slab or maybe 50mm Polyurethane + 13mm slab?

dunie001

Mind you the property was built at the turn of the 1900's so the allowed insulation value is probably just accounting for the unfrozen ground below...

I'm not sure what you mean by that but this is the way I would work that u-value out.

Use the following formula from TGD Part L to calculate the u-value of the floor. You would have most of the information already from other calculations you've already done in DEAP.

U = λ/(0.457B’ + dt),where
λ = thermal conductivity of unfrozen ground (W/mK) (this is 2.0)
B’ = 2A/P (m)
dt = w + λ(Rsi + Rf + Rse) (m)
A = floor area (m2)
P = heat loss perimeter (m)
w = wall thickness (m)

Rsi, Rf and Rse are internal surface resistance, floor
construction (including insulation) resistance and
external surface resistance respectively. Standard
values of Rsi and Rse for floors are given as 0.17
m2K/W and 0.04 m2K/W respectively. The standard
also states that the thermal resistance of dense
concrete slabs and thin floor coverings may be
ignored in the calculation and that the thermal
conductivity of the ground should be taken as 2.0
W/mK unless otherwise known or specified.

Ignoring the thermal resistance of the dense
concrete slab, the thermal resistance of the floor
construction (Rf) is equal to the thermal resistance
of the insulation alone

You should make a spreadsheet in Excel to use this formula, so in the future you only have to enter in the area, perimeter, insulation thickness and conductivity etc. etc. and then the spreadsheet will work out the rest for you.

Use the example given in the TGD Part L 2008 when making the spreadsheet, that way you can be damn sure it will be right!

I made one recently and it only took me around 10 or 15mins...but the time you will save when doing other assessments will be priceless...:D:);)

dunie001

the only way you could correctly determine that is by making a tiny hole in the plasterboard and sticking something small through until you hit the wall, then you will know exactly how thick the drylining is...

You might be able to figure it out from the window areas either because the drylining usually only goes to the edge of the window recess. But getting it accurate can be difficult...

Don't forget that you have to do Ru and Rl calculations to account for the timber battons as well. (see roof u-value calculations for the method)
You could determine the batten spacing by using a stud detector...

sinnerboy

dunie001 wrote: »

You should make a spreadsheet in Excel to use this formula, so in the future you only have to enter in the area, perimeter, insulation thickness and conductivity etc. etc. and then the spreadsheet will work out the rest for you.

Use the example given in the TGD Part L 2008 when making the spreadsheet, that way you can be damn sure it will be right!

I made one recently and it only took me around 10 or 15mins...but the time you will save when doing other assessments will be priceless...:D:);)

This software is a real chore saver

http://www.xtratherm.com/software/software.php