Insulating a house built with Cavity Bocks

J

joebloggs9669

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Not wanting to hijack the other thread which is about cavity walls this one is a query about a house built with those horrible Cavity blocks.

I live in one of these. It's in Dublin and many estates in the 70's and 80's were built with them. Its just a single cavity block plastered on both sides.

The house is not unexpectedly hard to heat and keep warm.

There appear to be 3 options open to me and I'm interested to see if anyone has tried option 3?

Option 1: Insulate inside. I've done this in some of the rooms..works well, takes away space from the room and hard to do some areas. 1K - 2K per room by time you redecorate.

Option 2: External Wraparound insulation. I can't do this because the side passageways are too narrow (wouldn't be able to fit the bin around the back/get a mini digger in if I did it. I'd have to get permission from neighbour to narrow his side passage also...(house is detached but I only own the passage at one side). Cost is in excess of 20K for 3 sides (front is brick with a proper cavity already filled with beads.)

Option 3: Pump the cavity blocks. I know this is not recommended (or at least not by the SEAI). I know it probably won't qualify for grants. I know it won't be as good as either of the other options but if it was a good bit better than doing nothing I would do it.. the cost is low....c2K. I have spoken to a provider of this who says it would make a big difference and claims to have done it many times. I know there will be loads of little holes in the walls but they will be replastered and I can easily paint the walls back to white.

Has anyone any real world experience of Option 3 they would be willing to share?

thanks in advance

Joe
 
Option 3 will do nought except lighten your wallet.
The salesman (provider) is selling.
 
We did Option 3 in the past on a previous house, it did make some difference but not to the same degree as full internal or external insulation would do. We did find a few cracks and gaps in places we didn't realise when the pump insulation came through them.

Is a combination of 1 and 2 a possiblity and if not done already, we did the attic floor and it made a big difference on a 2 story house
 
Thanks to both for your feedback

I can't do either side of the house with external wraparound but could do just the back...I was quoted 7K for that a few years ago so may consider it......If there is anyone else out there who has done Option 3 I'd love to hear your experience..
 
cavity block house here, I've never heard anything good about option 3. No supplier will have any documentation showing it's effectiveness at improving U values etc, because none exists, neither the SEAI or the UK equivalent has certified it as an insulation method. Every block is a cold bridge, and even if filling the cavities marginally improved the thermal performance of the wall, it's nigh on impossible to ensure that the columns are properly filled due to blockages etc.

FWIW I don't think external insulation is all it's cracked up to be either as any of my neighbours who have had it done (all by different contractors) it seems to be a half-assed job, with lots of missed sections and not going into the soffits or down to the ground.

I suspect doing it internally is the least bad option but as you've probably found out, disruptive and you lose space.

Consider your floors as well, we have suspended timber floors and they're a serious source of heat loss and draughts.
 
HI Shweeney

Thank you for that response.. I think I am convinced...and will stay away from Option 3.

I also have suspended timber floors and often wondered if anything could be done there without taking up all the floorboards which are mainly stuck under a mix of tiles, solid wood flooring and Laminate.. I know you need to have a draft flowing or the timber will rot....If anyone has any thoughts on what can be done I'd love to hear about it
 
The most appropriate solution depends on a number of factors and therefore there is no one size fits all answer. There may well be adequate solutions available without disturbing the floor itself. You are correct about the importance of the ventilation under the floor.
Having an on-site heat loss (incl air tightness test) survey done is valuable in this respect. One thing is certain though, adding insulation to the walls won't make a blind bit of difference if your heat loss is dominated by your (unsealed) suspended timber floor.
 
Just to put the above into context, I recently was called back to re-test a 2 storey house with a suspended timber floor after the recommended air tightness measures were carried out. The house initially tested at 13 m3/hr/m2 @50Pa (essentially 13 air changes per hour or an air change every 4.6 minutes with a 20 mph wind blowing outside). The 2nd test was 2.8 m3/hr/m2, a massive improvement and huge difference in heat retention. And the kicker is the client did the work himself and overall cost of material was <€2000. Majority of work was to the floors. Prior to the initial survey, the client was convinced that he would be spending 10's of '000's on insulation / new windows etc to improve things.
 
In a nutshell, he air tightened them and their junction to the walls using proprietary air tightness materials as advised during the initial test / survey.
 
I'm not an expert on this but common sense tells me do not go for option 3.
It only takes a tie between a cavity wall bridged with mortar to transmit damp across, with cavity block it has 100s of bridges across, if you cavity fill it you stop the circulation of air and very likely have damp problems
 
We did the internal Insulation with 50mm PIR and found a huge improvement.
For our suspended wooden floors, we used that foil bubble insulation. Put a layer of it over the floor, taped it to the wall, and then carpeted or floored over it as normal. Basically airsealed the floor.
 
Relatives had Option 3 done on their house years ago. I don't think it's made much difference at all. I don't know of any way Option 1 or 2 would work really. Neither are practical.
 
Options 1 & 2 work perfectly well when done properly.
What do you mean by "practical"?
It is clear that all insulation procedures will have consequences other than reducing heat loss
 
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