Insulation Again - Quickie though?

grassynoel

I've read the very informative threads on Cavity Wall insulation posted here but am looking for a quick opinion on the following please if ye can bear to go through it again

First off, am/have to at this stage going down the cavity wall route. My plans have a 110mm cavity. I got bamboozled and a bit scared about the dangers (mould, bad workmanship etc) of adding insulated plasterboard to improve the U-value so the question is

Would it be any use in maximising the cavity to put in 100mm (Kooltherm K8 or equivalent) and leaving the required 40mm air space. Can only use 70mm board in the designed 110mm Would this have any implications for my Planning Permission (not going through that again!!), wall ties, windows, hollowcore first floor and anything else apart from the cost of stronger foundations. Would 30mm cavity insulation extra justify additional costs???

I will probably pick and choose rooms to add insulated slabs also so was just wondering what ye thought on increasing the cavity width to accomodate thicker cavity wall insulation before the foundations are poured in relation to future proofing. Thanks and sorry for bringing it up again.

sydthebeat

grassynoel wrote: »

I've read the very informative threads on Cavity Wall insulation posted here but am looking for a quick opinion on the following please if ye can bear to go through it again

First off, am/have to at this stage going down the cavity wall route. My plans have a 110mm cavity. I got bamboozled and a bit scared about the dangers (mould, bad workmanship etc) of adding insulated plasterboard to improve the U-value so the question is

Would it be any use in maximising the cavity to put in 100mm (Kooltherm K8 or equivalent) and leaving the required 40mm air space. Can only use 70mm board in the designed 110mm Would this have any implications for my Planning Permission (not going through that again!!), wall ties, windows, hollowcore first floor and anything else apart from the cost of stronger foundations. Would 30mm cavity insulation extra justify additional costs???

I will probably pick and choose rooms to add insulated slabs also so was just wondering what ye thought on increasing the cavity width to accomodate thicker cavity wall insulation before the foundations are poured in relation to future proofing. Thanks and sorry for bringing it up again.

you dont need to pour wider or deeper foundations. In reality, the increase in cavity width doesnt increase the loading. The 3 x width rule for founds is only a simply rule of thumb.
the wider cavities have knock-on effects such as more ties, changes in ope details, closings etc, but these are simply a case of getting them correctly rather than adding any significant cost onto you.

It would be a better idea to use 100 AAC blocks as the inner leaf (150 if a concrete floor is being used)... but obviously this is a more expensive option.

sinnerboy

grassynoel wrote: »

hollowcore first floor .

do you have an engineer ? - hc slabs require 215 inner leaf to bear on

i would suggest 60mm foil faced pu (ffpu) in 100 cavity and dry line
25 x 50 battens
40 ffpu , tape joints
polythene
plasterboard
place 25 ffpu behind elec points to

tape seal window frames to block work before plasterboard

tape seal all services penetrations

ask air tightness tester to do pre test inspection - when roof is on , windows in before plasterboard and then
return to test before decorations


OR

can you consider 215 solid block ( no cavity ) with external insulation + render - even better

Slates

sinnerboy wrote: »

do you have an engineer ? - hc slabs require 215 inner leaf to bear on

They only need a 100mm wall, 215mm needed where to slabs are meeting

sinnerboy

the actual factory produced pc unit needs only 100 to bear on - that is true

however the pc units assembled together on site must be tied together with screed poured over the top of the units and then the screed must turn continuously down the sides of the unit , min 100mm at the side , reinforced to form a composite floor plate .

ergo - pc units must be rested on 215 walls

To the OP I say - it really doesn't matter what ANYONE posts here - I hope you have appointed a structural engineer to certify

Slates

:

sinnerboy wrote: »

To the OP I say - it really doesn't matter what ANYONE posts here - I hope you have appointed a structural engineer to certify

To right, you dont want €6000 worth of material to come crashing down :eek:

sydthebeat

some precast concrete (wide) slabs only require 100 inner leaf,

most (if not all) hollowcore slabs require 215 inner leaf
http://www.edenprecast.ie/products.asp?cat=11&product=10

bauderline

I am getting pc floors from Floods, they will be tied together with structural screed on top. Their engineer requested a number of my internal walls to be changed to 215 blocks... Apparently you need this type of flooring if you want to use UFH, so thats another you would want to check with the supplier / engineer.

BL.

ollie30

spanwright specified only walls that slabs meet to be 215mm in my case all other walls the normal 100mm

grassynoel

Had given the plans to the hollowcore company and they said they were ok to take 200mm hc and 75mm screed. Got that quote a while back so will have to talk to them again to clarify. I presume the HC spans the 2 leaves and cavity? The blocklayer thought one internal wall needed to be wider alright. Architect drew the Plans and will get his advice on the insulation also (think he did the BER thing recently also).

Can I trust the Architect to have designed the loading for the hollowcore correctly? ie would he be responsible if I followed his spec. precisely and something went wrong. I don't think he has an engineer working for him? Is this ultimately a call for an Engineer is what Im trying to say? I see he has written 'to Engineers details' on the plans in relation to the subfloor but not for the first floor.

Anyways, I will get the hollowcore floor supplier to ok the Plans first. Planning the Insulation and getting it right is wrecking my head, don't get me started on heating. Thanks for the replies

grassynoel

Ooops presumed wrong for hc spanning both leaves

muffler

grassynoel wrote: »

Ooops presumed wrong for hc spanning both leaves

Thats OK. Im drunk too.

sinnerboy

grassynoel wrote: »

Had given the plans to the hollowcore company and they said they were ok to take 200mm hc and 75mm screed. Got that quote a while back so will have to talk to them again to clarify. I presume the HC spans the 2 leaves and cavity? The blocklayer thought one internal wall needed to be wider alright. Architect drew the Plans and will get his advice on the insulation also (think he did the BER thing recently also).

Can I trust the Architect to have designed the loading for the hollowcore correctly? ie would he be responsible if I followed his spec. precisely and something went wrong. I don't think he has an engineer working for him? Is this ultimately a call for an Engineer is what Im trying to say? I see he has written 'to Engineers details' on the plans in relation to the subfloor but not for the first floor.

Anyways, I will get the hollowcore floor supplier to ok the Plans first. Planning the Insulation and getting it right is wrecking my head, don't get me started on heating. Thanks for the replies

YOU must appoint a structural engineer to sign off on the structural aspects

• not the architect
• not the floorslab provider
• not any one posting here