Cold bridging v Thermal mass with internal block walls

Bobby04 · 11-12-2010 09:21PM #1

I am confused about the effect of having a plastered internal block wall. On the one hand I can see how it's thermal mass potential could be beneficial. But on the other hand I assume it is a huge cold bridge since it is blockwork built on the foundations with no insulation seperating it from the cold ground. So could anyone kindly explain how this cold bridge effect is deemed to be irrelevent compared to the benefits associated with the thermal mass effect?

sinnerboy · 12-12-2010 11:19AM

The cold bridge should be minimized . You can bring up the rising walls to DPC in AAC blocks
( Quinn Lites ) . Or use a Foamglass course below DPC . Or use an insulated raft and avoid the cold bridge entirely . Or use a stud partition .

A low thermal mass building will heat up and cool down quickly .
A high thermal mass building will heat up and cool down slowly .
Whether this is good or bad depends on how you live .

A block wall will absorb heat and release it later . If it is absorbing heat when you want it and releasing it later when your not there ( as in case of the morning heating period for two adult workers no kids ) . But if the house is not left empty for hours on a regular basis then high Thermal Mass may help to moderate sudden temp drops .

Bobby04 · 12-12-2010 10:08PM

sinnerboy wrote: »

The cold bridge should be minimized . You can bring up the rising walls to DPC in AAC blocks
( Quinn Lites ) . Or use a Foamglass course below DPC . Or use an insulated raft and avoid the cold bridge entirely .

Thanks sinnerboy.

So I guess I'm right that there is an issue of cold bridge if you don't somehow minimise it as outlined above. I've no doubt my knowledge of building methods is seriously outdated now, but I have never heard of any of the above mentioned methods being used with internal block walls before! Am I right to suspect that not many people take this cold bridge into consideration??

sinnerboy · 12-12-2010 10:57PM

Yes you are . ( Apart from regular posters here ) . 10 /10 to you for engaging the grey matter

cuculainn · 13-12-2010 12:42PM

sinnerboy wrote: »

A block wall will absorb heat and release it later . If it is absorbing heat when you want it and releasing it later when your not there ( as in case of the morning heating period for two adult workers no kids ) . But if the house is not left empty for hours on a regular basis then high Thermal Mass may help to moderate sudden temp drops .

Sorry for jumping in on this thread, but does anyone know the thermal mass of a concrete block? i have heard that it is pretty poor really.....so just wondering what level of thermal storage do regular blocks supply?

BTW I do realise that it will be more than insulated slabs

sydthebeat · 13-12-2010 01:42PM

cuculainn wrote: »

Sorry for jumping in on this thread, but does anyone know the thermal mass of a concrete block? i have heard that it is pretty poor really.....so just wondering what level of thermal storage do regular blocks supply?

BTW I do realise that it will be more than insulated slabs

its not really all about thermal mass, its more important to consider the diffusivity of the material. this is the relationship between the thermal mass and the time lag to release the heat back out. idealy, so ive been told, that a time lag of 12 hrs is preferrable for your material, so it is "soaking up" heat at its quickest rate at say 2:00 pm and is releasing at its quickest rate at 2:00 am. Ive beenled to believe that while concrete has a high thermal mass, it had a bad thermal lag in that it releases its stored heat very quickly when compared to other high density products.

Concrete can exist in many different densities. (Stanard concrete blocks are around 1800 kg/m3)

cuculainn · 21-02-2011 11:21AM

sydthebeat wrote: »

its not really all about thermal mass, its more important to consider the diffusivity of the material. this is the relationship between the thermal mass and the time lag to release the heat back out. idealy, so ive been told, that a time lag of 12 hrs is preferrable for your material, so it is "soaking up" heat at its quickest rate at say 2:00 pm and is releasing at its quickest rate at 2:00 am. Ive beenled to believe that while concrete has a high thermal mass, it had a bad thermal lag in that it releases its stored heat very quickly when compared to other high density products.

Concrete can exist in many different densities. (Stanard concrete blocks are around 1800 kg/m3)

Hi I am resurecting this discussion again!.

So while a standard block has good thermal mass it releases the heat relatively quickly. This could be good or bad really. If your heating ramps down at 8 pm say, the blocks could release the heat to keep the living area warm till 10 pm at which point it is bed time!!

Which potentially would be better than having it release the heat at 2am when it is not needed. But there are other situations when a longer release time would be better im sure.

Slightly changing topic, we are currently at our plastering stage.
We have internal block walls. We have a row of AAC blocks to break the cold bridge between the raft and the wall.

Our plasterer is recommending to dryline with isulated slabs (external walls only) We initially thought it was a good idea but are now thinking that it is not.

We have 150mm pumped cavity which should give a Uvalue of 0.2.
Is there a benifit in drylining?
Considering it will cost about €5000, what heat savings will be made?
If it saved us €100 euro a year ( I doubt it would) that would be a minimum 50 yr payback, which does not make sense.

Also we are going with a low temp heat pump so maybe the thermal mass of the block would be more benifical?

On the other hand we only have one shot at this an maybe we should aim to bring the wall U-value down to as low as possible

Cold bridging v Thermal mass with internal block walls

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