wall construction- cavity

ruskin

Hi
Has anyone here ever used a 150 wide cavity in their external wall construction? If so, could you please tell me about it (any photos) and what the potential benefits are? Ive been told from my engineer that that the 150 cavity allows more insulation to be put in the cavity and thus helps the BER.

sydthebeat

ruskin wrote: »

Hi
Has anyone here ever used a 150 wide cavity in their external wall construction? If so, could you please tell me about it (any photos) and what the potential benefits are? Ive been told from my engineer that that the 150 cavity allows more insulation to be put in the cavity and thus helps the BER.

that is correct.

the general consensus is that you need to retain a 40-50mm cavity, therefore if you want to increase you insulation specification you can either:

externally insulate
increase insulation in the cavity, ie install 100mm
or insulate internally with insulated plasterboard.

insulating internally leaves many areas that are somewhat exposed
ie if you have 60mm incavity and another 40mm internally, then at all junctions between internal and external blockwalls, junctions between floors and external walls you dont have 100mm insulation, you only have 60........ some people are happy with this...

again, there is a consensus that any cavitys over 150mm needs to be designed by specialist enginners...

sinnerboy

Recently did a 120 cavity
40 air space
80 insulation
together with 25+12 insulated board dry lining

However ....
The cavity board workmanship was poor . Despite repeated snaggings the contractor built floor to wall plate with

1. mortar droppings across horizontal t+g joints that did consequently not t+g
2. 5-6mm gaps at vertical but joints
3. lintol ends at corners projecting into cavity like a granny's elbow on a packed bus ( he was made grind them away )
4. cavity boards leaning away from internal leaf

all of which allows cold cavity air to circulate behind the insulation board and devalue it's performance

The 80mm board will perform to the same thickness as a ( correctly installed ) 55mm board

The contractors reward - he is now putting up 50+12 insulated board - extra cost his problem

MORAL - watch the workmanship . A silk purse can be turned into a sows ear

gally74

Mod edit: I have moved your post to a new thread here

budo73

gally74 wrote: »

hello all,

i have built the shell now with a 100 mm cavity, 60 mm insulation,

i was talking to a heat recovery installer and he said i should pump the rest of the cavity, he said if there are any gaps between the insulationm then its kind of useless,

any idea's on this, given sinnerboys post on uk standards, i am now concerned about the hollow core junction and the outer leaf aswell, so i am thinking of pumping the cavity,

i am also thinking of doig the insulated slab on the inside, still havent decided on this,

any commnets or advice appreciated,

Hi

I would advise you against this. In the UK it is reasonably common to use a fully filled cavity as you are suggesting. The general consensus is, however, that a partial fill is better. Our standards in terms of insulation (and in a couple of other areas) are actually superior to the UK standards.

If you fully fill the cavity you are facilitating cold bridging and the flow of damp if something goes wrong (i.e. there is a small gap in the fill or mortar droppings have built up).

If you want to see more then go into a book shop and pick up a copy of Homebonds House Building manual. This basically summarises the Irish standards.

Budo

budo73

sorry, forgot to say....

If you really want to improve the insultation, then put some on the inside and dryline over it, this is defintely the best option.

gally74

thanks budo,

ruskin

<SNIP>

I don't mean to be rude, but your query has nothing to do with the reasoning behind this thread. Are there any architects out there using a 150 cavity in their external walls?


Mod edit: Sorted

muffler

Can we get back on topic again please - discussion about 150mm cavity.

Slig

As syd said, 150mm cavity should definately be designed by a specialist. In a standard 300mm cavity wall the theory is that the 2 leafs act as a composite over the 100mm cavity. By increasing the cavity you are increasing the gap between the blocks and encouraging it to act less like a composite unit and more like 2 independant 100mm walls and a 100mm blockwork wall is deceptively shakey.
If you wish to do this correctly then increase your inner leaf to a 215 block (block on flat) and use this as your structure completely,support floors, wall plate etc., the outer leaf should then only be a rainscreen, if you are cladding with stone then using this method you could even omit the blockwork outerleaf behind the stone.
Remember though from a practical point of view, with an enlarged cavity you will need larger cills, specialist lintels, longer wall ties, bigger door frames etc. which will all add to the cost.

mdinee01

" The contractors reward - he is now putting up 50+12 insulated board - extra cost his problem "



Did you have a thermal camera to show the poor workmanship or what ?

how did you enforce that builder to do the remediation work, did you have such a clause in the contract (and how was it worded) ?

interested from point of drawing up my own contract specs for a house build.

sinnerboy

no thermal camera . horizontal joints in insulation forced apart by mortar droppings , vertical joints not cut straight and true and insulation slabs leaning foward from inner leaf was all clearly visible during works progress . result - cold cavity air can circulate behind the insulation and de value its performance

when specifying a buidling element , after you list its component parts - state the required u value . the contarctor is then CONTRACTED to that

as for enforcement - sadly , so often , money talks . you withold payment for works that are not compliant with the contract