Full fill cavity bead insulation problem?

KevMayo88

We are going with full-fill platinum bead insulation in our 150 cavities of our external walls. I was looking at my window details, and over the head of each window is shown a 'stepped dpc'. How is the full fill supposed to work with this? As I see it, the insulation will be blown into the cavity, but won't the stepped dpc will block the full fill from being allowed to fill the area beneath the stepped dpc?

10-10-20

My thinking is that the stepped DPC is laid over the insulated steel lintel (such as below) with the DPC sloping outwards to the external leaf?

https://www.goodwins.ie/products/Steel-Cavity-Lintel-3600mm-S-K-90.html?filter_set%5B%5D=1,92,579

Can you photograph the detail so that we can review?

KevMayo88

https://www.boards.ie/discussion/comment/120574579#Comment_120574579

My window details are similar to the above- concrete lintels with a stepped dpc over (in blue there). I'm worried that the triangle area under the dpc wont get filled with bead insulation

10-10-20

Correct, it won't.

Plus it's probably not so precisely sloped as curved. But in my mind it's nothing much to worry about as the cavity will no longer be the big convector and the overall loss at the wail will be significantly reduced. I'd like to hear other opinions on it too.

Biker1

https://www.boards.ie/discussion/2058295805/full-fill-cavity-bead-insulation-problem

Assuming it's a new build then they will be drilling from the inside so just make sure they drill extra holes just above the lintels to fill that triangle. As 150mm bead wont meet the regs you will need to use insulated slabs to the interior.

KevMayo88

https://www.boards.ie/discussion/comment/120575079#Comment_120575079

Holes above my lintel? I dont like the sound of that! My architect has said in addition to the full fill I need to go with a 50mm insulated slab, but I think this is complete overkill, as the full fill bead will be 150mm thick once complete. The full fill should give me a great U value even without drylining.

muffler

https://www.boards.ie/discussion/comment/120575263#Comment_120575263

and you have your technical data to back this up?

KevMayo88

https://www.boards.ie/discussion/comment/120575366#Comment_120575366

Yes, I rang a bead insulation company who informed me that internal drylining is not required with a full fill cavity.

Biker1

https://www.boards.ie/discussion/comment/120575525#Comment_120575525

So you are taking advise from the sales people !!!. In order to meet the backstop u-value of 0.18w/mk you have either to increase the width of the cavity or install drylining. If you engage a BER assessor they will outline the exact requirements for compliance with Part L.

Yellow_Fern

Shame that you have to dryline. That will really undermine the battery effect of the mass of the concrete.

KevMayo88

So I spoke to an engineer this evening who said in relation to my original query that what is normally done under a stepped dpc with bead insulation is that this triagular void is filled with mineral wool. He also agreed with my architect and said I would require insulated drylining internally. When I told him the bead company person did not believe this to be necessary, he told me in no uncertain words that he felt they were wrong!

muffler

https://www.boards.ie/discussion/comment/120575525#Comment_120575525

So you were quite happy to take the word of a salesman over the word of your architect?

chooseusername

https://www.boards.ie/discussion/comment/120576525#Comment_120576525

And you're quite happy to jump in without reading subsequent posts!

bfclancy2

https://www.boards.ie/discussion/comment/120576525#Comment_120576525

i wouldn't be too happy with an architect that specced a cavity that couldn't meet requirements and requires an internal insulated slab thereby eliminating the thermal mass benefit of the blockwork

KevMayo88

https://www.boards.ie/discussion/comment/120578098#Comment_120578098

Then you wouldnt be happy with alot of architects- full fill bead and insulated drylining is a very common practice. My architect said that this idea of thermal mass benefit is nonsense.

Biker1

While the practice of dry lining new houses is common in certain parts of the country it is far from best practice or cost effective. You still have to plaster the block work to form an airtight layer. Rarely is the dry lining extended up to the hollowcore thereby creating a huge thermal bridging area in the ceiling void. Also, all the junctions of internal walls and cavity walls would have a thermal bridging issue. Despite what your architect says thermal mass can have a significant effect on comfort levels within the house. This effect depends greatly on the design.

bfclancy2

https://www.boards.ie/discussion/comment/120578383#Comment_120578383

its an outdated practice, thermal mass benefit is obvious, thats why underfloor heating works, get a new architect

sydthebeat

the answer is quite simple if the designer of that window head detail actually understood how to build the actual detail.