Hi, I'm currently building a 2-storey extension to my cottage. Up to first floor height the inner-leaf has been built using 7N blocks as it forms part of a retaining wall on 3 sides. However as we build up past the first floor I have a choice of using thermolite blocks or 3.5N medium blocks. Can anyone tell me which route to choose as I have to order the materials to crack on with the project. I understand thermolites have a better insulation factor but feel that the 3.5N medium blocks are more robust. Please help, many thanks
Which blocks to use
- Thread starter clarebear
- Start date
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Yes some homeowners dispise their thermolights since it is harder to make fixings in them thqt stay put.
You have not stated the wall construction stats, ie the width of bricks/ blocks etc, the cavity gap, insualtion being used in cavity and the design U value so we cannot comment as to how much the U value would be improved by differnt inner block choice.
Also turbos are 2.8, shield 2000 4, and Hi-strengh are 7 in thermolight (BTW the names have changed - but my pocket guide has not)
So it looks to me like you are already using airarted blocks ie thermolights
Over to you...
You have not stated the wall construction stats, ie the width of bricks/ blocks etc, the cavity gap, insualtion being used in cavity and the design U value so we cannot comment as to how much the U value would be improved by differnt inner block choice.
Also turbos are 2.8, shield 2000 4, and Hi-strengh are 7 in thermolight (BTW the names have changed - but my pocket guide has not)
So it looks to me like you are already using airarted blocks ie thermolights
Over to you...
The ground floor is already built. The inner and outer leaf are constructed from 100mm Dense Solid 7.3N Blocks and the 100mm cavity is filled with reinforcing bar and concrete (as the building is back-filled with earth up to the first floor level).
The build then turns into what I would call a 'normal' build at first floor level. On my spec sheet it says external walls are to be 112mm facing bricks (am using reclaimed), 100mm cavity filled with Dritherm insulation or similar, 100mm insulating blocks (thermolite). But it has been suggested that instead of the thermolites I could use 3.5N medium blocks. I don't really know which way to turn.
The build then turns into what I would call a 'normal' build at first floor level. On my spec sheet it says external walls are to be 112mm facing bricks (am using reclaimed), 100mm cavity filled with Dritherm insulation or similar, 100mm insulating blocks (thermolite). But it has been suggested that instead of the thermolites I could use 3.5N medium blocks. I don't really know which way to turn.
Aerated blocks are easier to lay, will provide better thermal insulation but are more expensive and prone to cracking. That's not really material though - thousands of houses are built from them, many crack and it's not a great problem unless the cracks end up 15mm wide in which case the problem ain't with the blocks it's something else.
Concrete blocks are more difficult to lay, provide lower thermal insulation but are cheaper and don't tend to crack.
The only thing you need to double check is that 100mm Dritherm with the conkers satisfies the minimum U-value requirement. (but off the top of my head I think it does)
Concrete blocks are more difficult to lay, provide lower thermal insulation but are cheaper and don't tend to crack.
The only thing you need to double check is that 100mm Dritherm with the conkers satisfies the minimum U-value requirement. (but off the top of my head I think it does)
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Thanks John, that's been very helpful. I think we will probably use thermolite because of the insulation value and because everyone keeps telling me to shut-up about blocks! Out of interest which would you choose?
I always prefer a lightweight concrete block.
These can be just as light as thermalites, but are easier to lay (perp joints stick better and bed joints don't dry out as fast), and they don't dry out as quick - so less prone to early cracking.
Also, more tolerant of post-setting movement - so less prone to thermal cracking, and take fixings better.
Yes, concrete may be less thermally efficient, but you are presumably keeping a wide cavity with nsualtion, so the wall will perform to current regs in any case - so this is not a big issue.
These can be just as light as thermalites, but are easier to lay (perp joints stick better and bed joints don't dry out as fast), and they don't dry out as quick - so less prone to early cracking.
Also, more tolerant of post-setting movement - so less prone to thermal cracking, and take fixings better.
Yes, concrete may be less thermally efficient, but you are presumably keeping a wide cavity with nsualtion, so the wall will perform to current regs in any case - so this is not a big issue.
Why don't you look up the R values for the components in the wall and do the U value calculaltions using different types of blocks and post your answers here?
Its very easy once you know how: http://www.concrete.org.uk/fingertips_nuggets.asp?cmd=display&id=598
Hi! Not sure why the architect/designer is going for a filled cavity, its always best to have a clear cavity to allow the external brickwork to breathe on the inside of the cavity. I know cavity fill is used quite a lot, but I wonder if people realise that the thermal performance of the insulation material suffers as a consequence either through rainwater penetration and/or thermal bridging in cold weather.
A much improved solution, would be the following:
19mm Lightweight Internal Plaster Finish
100mm Thermalite Turbo
50mm PIR Insulation (Conductivity (k)=0.023W/mK)
50mm Cavity
External Brickwork
Calculation follows:
Thermal Resistance 'R' (m2K/W)
Rsi + Rso = 0.18
Plaster = 0.032
Lightweigt block = 0.91
Insulation = 2.174
Cavity = 0.18
External Brickwork = 0.13
Total Thermal Resistance (R) = 3.606
U value (Thermal Transmittance) = 1/R = 1/3.606
U value = 0.27W/m2K
Which would meet the requirements of Part L of the Building Regulations, and give you a hopefully dry cavity.
I hope the above helps you in your decision
Regards
A much improved solution, would be the following:
19mm Lightweight Internal Plaster Finish
100mm Thermalite Turbo
50mm PIR Insulation (Conductivity (k)=0.023W/mK)
50mm Cavity
External Brickwork
Calculation follows:
Thermal Resistance 'R' (m2K/W)
Rsi + Rso = 0.18
Plaster = 0.032
Lightweigt block = 0.91
Insulation = 2.174
Cavity = 0.18
External Brickwork = 0.13
Total Thermal Resistance (R) = 3.606
U value (Thermal Transmittance) = 1/R = 1/3.606
U value = 0.27W/m2K
Which would meet the requirements of Part L of the Building Regulations, and give you a hopefully dry cavity.
I hope the above helps you in your decision
Regards
I agree, as long as the bricky doesn't fill it up with snots, crisp packets, coke cans etc!
Thanks for saving me the trouble to look up the figures ALR
But I'm not too keen on lightweight blocks such as turbos since they are a swine to fix to.
If I was to build an extenstion here in Middlsex I might:
19mm Lightweight Internal Plaster Finish
Internal Brickwork/ non airated block
100mm PIR Insulation (Conductivity (k)=0.02875W/mK with 20% aging factor applied)
External Brickwork
Calculation follows:
Thermal Resistance 'R' (m2K/W)
Rsi + Rso = 0.18
Plaster = 0.032
Internal Brickwork = 0.13
Insulation = 3.47
External Brickwork = 0.13
Total Thermal Resistance (R) = 3.942
U value (Thermal Transmittance) = 1/R = 1/3.942
U value = 0.25W/m2K
Only a slight improvement in U value over ALR but I have aged the PIR by 20% as I have asumed his K value is for virgin materal. But I have easy fixing into bricks and higher thermal inertia internaly
But I'm not too keen on lightweight blocks such as turbos since they are a swine to fix to.
If I was to build an extenstion here in Middlsex I might:
19mm Lightweight Internal Plaster Finish
Internal Brickwork/ non airated block
100mm PIR Insulation (Conductivity (k)=0.02875W/mK with 20% aging factor applied)
External Brickwork
Calculation follows:
Thermal Resistance 'R' (m2K/W)
Rsi + Rso = 0.18
Plaster = 0.032
Internal Brickwork = 0.13
Insulation = 3.47
External Brickwork = 0.13
Total Thermal Resistance (R) = 3.942
U value (Thermal Transmittance) = 1/R = 1/3.942
U value = 0.25W/m2K
Only a slight improvement in U value over ALR but I have aged the PIR by 20% as I have asumed his K value is for virgin materal. But I have easy fixing into bricks and higher thermal inertia internaly
Are you implying my calcualtions are nothing more than hot air?
Why the paranoia with aerated blocks?
I have gallows brackets supporting shelving, fixed to them in my garage with serious weight atop. All you need is common sense FFS!
Drill a smaller hole than recommended. Use decent plugs. Don't use hammer on the drill and don't clear the bit to much either.
I have gallows brackets supporting shelving, fixed to them in my garage with serious weight atop. All you need is common sense FFS!
Drill a smaller hole than recommended. Use decent plugs. Don't use hammer on the drill and don't clear the bit to much either.
There are cetain people who consider a masionry built structure should have some weight to it and blocks that float in water aint heavy!
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