cavity block vs cavity wall

fruitbats

I apologise if this has been on forumrecently but I really need to know as I’m not sure if my builder is telling methe truth and he’s starting digging the foundations soon?

So anyway

He says there is no difference between a 225mmcavity block wall with 62mm insulation board and that of a cavity wall(insulation in the middle)l?

All he says is the cavity wall is twice theprice and no real benefit.

So if both walls are constructed properly,is there much difference between the two or enough reason to go with one over the other ?

Thanks in advance as my head is wrecked andI really need somebody that knows whatthey talking about.

Outkast_IRE

Can i ask your building a house and you dont know the wall construction ?
Have you hired an architect or do you have any sort of plans to work from.

There is a massive difference between a cavity wall with the correct insualtion in the middle in comparison to cavity block with internal insulating board.

Honestly this builder doesnt sound like he has a clue. I dont like saying walk away from him now, but if this the sort of opinion he has, then he is beyond clueless.

Im strongly urging you to make use of an architect or architectural technician at least to point you in the right direction.

I doubt if a cavity block with 62mm of insulation would even come near to current Minimum building regulations, to me alarm bells are ringing here.

If building a cavity wall what size gap are you leaving between the inner and outer to accomodate insulation ? Please seek some professional guidance now.

fruitbats

thanks , it a house extension, it only about 27 sq metre's. he siad he would do it with cavity block to keep the cost down as a cavity wall would be twice the price?

Outkast_IRE

fruitbats wrote: »

thanks , it a house extension, it only about 27 sq metre's. he siad he would do it with cavity block to keep the cost down as a cavity wall would be twice the price?

Look honestly take this advice from someone with nothing to gain or lose by you.

Hire a professional to make up a proper set of plans to work from. You wont regret it you will end up with a well insulated, well thought out extension.

I honestly dont like the sound of your builder one bit, if he doesnt understand the potential problems with using cavity blocks and drylining the inside then i wouldnt want him near my site.

The only reason drylining is even considered is due to its retrofitting ease. I would never suggest it in a new build or extension. i cant comment on the price of cavity block vs cavity wall.
He would save you money alright in the short term, but i would counter that you would see similar savings longterm with a well insulated well designed extension.

Also if you do get some professional help see if they can reccomend a Q.S they are great at breaking the costs down with a proper set of plans and ensuring your getting value for money.

sydthebeat

cavity block drylined is the cheapest and, in my opinion, the lowest quality build method thats acceptable.
Id echo the above post and say i never recommend in unless its a case of a budget cut to the bone.

Its main advantage is the speed of construction, the relative low skill need to build it, and the lower cost.

Its main disadvantage is the inherent problems. No cavity, Thermal bridges, no stepped DPCs.

In my experience cavity block DOES NOT cost 50% that of cavity wall.
Perhaps 10-15% less at a push.

PS dont let a builder tell you what the specification will be. You should tell the builder and get him to price accordingly. In that way you can get minimum 3 prices where everyone is pricing for the same thing.
It goes without saying that if you dont know how to compile the specification you should hire someone that can.

fruitbats

sydthebeat wrote: »

cavity block drylined is the cheapest and, in my opinion, the lowest quality build method thats acceptable.
Id echo the above post and say i never recommend in unless its a case of a budget cut to the bone.

Its main advantage is the speed of construction, the relative low skill need to build it, and the lower cost.

Its main disadvantage is the inherent problems. No cavity, Thermal bridges, no stepped DPCs.

In my experience cavity block DOES NOT cost 50% that of cavity wall.
Perhaps 10-15% less at a push.

PS dont let a builder tell you what the specification will be. You should tell the builder and get him to price accordingly. In that way you can get minimum 3 prices where everyone is pricing for the same thing.
It goes without saying that if you dont know how to compile the specification you should hire someone that can.

thanks this is very helpfull, So it would only generally cost 10-15% more for a cavity wall, I'll keep that in mind when he comes back to me with the quote?

newmug

He hasn't even given you a quote yet and you're letting him start digging the foundations:eek:

I've seen plenty of extensions built both ways. Nothing wrong with cavity blocks, if that's what you want. Then again, there's nothing wrong with living in a tent, if that's what you want! But if it was me, and I was only doing it once, I'd go for cavity walls.

fruitbats

newmug wrote: »

He hasn't even given you a quote yet and you're letting him start digging the foundations:eek:

I've seen plenty of extensions built both ways. Nothing wrong with cavity blocks, if that's what you want. Then again, there's nothing wrong with living in a tent, if that's what you want! But if it was me, and I was only doing it once, I'd go for cavity walls.

thanks, i have a quote for the cavity block but not for the cavity wall, again i didn't know enough about it to be what way he is going to do it , to as the correct questions.
anyway i was looking on the internet and it got me all worried about my options!!

newmug

fruitbats wrote: »

thanks, i have a quote for the cavity block but not for the cavity wall, again i didn't know enough about it to be what way he is going to do it , to as the correct questions.
anyway i was looking on the internet and it got me all worried about my options!!

Ah don't worry. If he hasn't started yet, you're grand. You can always get other quotes off other fellas, you don't have to let this lad know. Anyway, if you really, really, really, really had to go with cavity blocks, it wouldn't be the end of the world. Personally, I wouldn't though, for all you'd save in an extension that size.

belcampprisoner

http://www.seai.ie/Power_of_One/FAQ/Insulation/What_is_9%E2%80%9D_Cavity_Block_Insulation.html


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fruitbats

Anyway it looks like I'll holding off on the extension until I can afford a cavity wall. I take it that this is the best option for an extension? and just out of curiousity, what thickness of insulation should be used for the cavity? also if anyone knows, is 70 mm kingspan suitible for the floor and ceiling or should it be 100mm?
thanks, you've all been a great help!!

totallegend

fruitbats wrote: »

Anyway it looks like I'll holding off on the extension until I can afford a cavity wall. I take it that this is the best option for an extension? and just out of curiousity, what thickness of insulation should be used for the cavity? also if anyone knows, is 70 mm kingspan suitible for the floor and ceiling or should it be 100mm?
thanks, you've all been a great help!!

Can I piggyback on this query too?

I think I've seen 100 - 120 mm being mentioned as being the thickness of insulation required, so how thick would the final wall be from the outer surface to the interior?

We're hoping to put on an extension but it's a terraced house so if the walls end up being very thick, we're going to lose a fair bit of space and we need to reconsider.

DOCARCH

totallegend wrote: »

I think I've seen 100 - 120 mm being mentioned as being the thickness of insulation required, so how thick would the final wall be from the outer surface to the interior?

360mm...well, that's my default extension wall thickness these days (with 125mm full-filled cavity).

You could reduce that thickness by considering timber frame (but you also then have to consider fire safety/distance from boundaries).

totallegend

DOCARCH wrote: »

360mm...well, that's my default extension wall thickness these days (with 125mm full-filled cavity).

You could reduce that thickness by considering timber frame (but you also then have to consider fire safety/distance from boundaries).

Great, thanks

Timber not an option I'm afraid