insulation and air tightness membrane

Audioslaven

Hi,

I installed 100mm rafter loc between the joists(6*2 50mm gap to the felt) then installed a isover airtightness membrane over this on the warm side of the rafter loc and intend to install 100mm xtratherm insulated slab(foiled back) over the isover membrane. As both insulations are foiled back between the isover membrane, will i get a build up of moisture on the isover membrane leading to issues down the road with mold and rot?

Any info appreciates

sinnerboy

The essential technical "cleverness" of these air tight membranes is that is summer months they become vapour open - allowing moisture to migrate into the building .

If you use a solid foam type insulation below the membrane then moisture will be trapped as those insulations are vapor tight .

I would batten across your rafters using Rockwool in between .

Bear in mind that whatever you decide to do you must not sandwich electrical cables in between insulation layers as they can over heat and catch fire .

Audioslaven

Cheers sinnerboy,

there are no services so I will have no issues there. I have just applied the air tightness membrane from the ceiling down below to about 3 inches onto the wall about 1 meter altogether. The house is a storey and half and I just want to make sure the rooms are not cold around the dormer windows.

sinnerboy

That system , Vario , also includes tapes specifically designed to seal window frames to the wall before you plaster .

1. If you use it and
2. pay attention to seal all openings in the external wall - pay special attention to drains from bathrooms and kitchens
3. apply a silicone bead to the bottom edge of each skirting board before you offer up for fixing

you can look forward to a decent air permeability test result . I would be hoping for around Q50 /5 .

gears

sinnerboy wrote: »

[*]apply a silicone bead to the bottom edge of each skirting board before you offer up for fixing
[/LIST]

you can look forward to a decent air permeability test result . I would be hoping for around Q50 /5 .

Can I ask why you feel the need for this step?

sinnerboy

1. because I have seen / felt air infiltration at skirting bases during air permeability tests
2. it is building regs guidance which you will find here http://www.environ.ie/en/TGD/

(scroll down to the set of Acceptable Construction Details )

gears

Point taken S.B. but doesn't silicone shrink and breakdown over time.

I think that the membrane should be sealed to the wall using the systems mastic (Vario DS Mastic or SIGA Primur). If this is done it doesn't matter what you do with your skirting board, IMHO.

sinnerboy

Touche gears - point like wise taken .

Main thing to note is that the base of the skirting is a weak spot . Be aware of that and do something about it .

soldsold

Isn't carpet normally tucked in under skirting boards? So a bead of silicon under the board might end up with a hairy edged carpet?

Tape manufacturers do a wide tape (around 150mm) that tapes the finished floor to the plastered external wall, with primer painted onto the floor first to make it more sticky.

Im more than willing to be corrected on the above though...

sas

soldsold wrote: »

Isn't carpet normally tucked in under skirting boards?

Not if the skirting boards were fitted properly in the first place

sinnerboy

+1

You see carpets tucked under skirtings typically in older properties where the skirting has shrunk after central heating was first installed

It can happen in new builds too

1. due to poor workmanship and/or
2. where properly dried skirtings are not used and/or
3. where skirtings are allowed to become damp on site due to poor storage conditions and/or
4. skirtings are installed too soon into the build when walls / plaster have not been given time to dry

So - seal them at the base !

I used the term "silicone" in the generic sense - I should really have stated "sealant" there are many different types of sealants so contact manufacturers to select the correct one for the application

.

soldsold

I put down (spray glued) a carpet last year and a wide cold chisel was the perfect tool to tuck the carpet under the skirting board, gave a nice neat fit with no bulging. I thought this was normal, even patted myself on the back when I was done.

Definitely would have struggled to get a neat edge finish if I had a skirting board touching the ground.

Similar results with laminate flooring a few years back, laminate went down first then skirting fitted on top. How do you fit laminate or wood flooring any other way if the skirting touches the ground?

Steve

sas

soldsold wrote: »

Similar results with laminate flooring a few years back, laminate went down first then skirting fitted on top. How do you fit laminate or wood flooring any other way if the skirting touches the ground?

Steve

For anything other than carpet it's preferable to remove the skirting and replace after the flooring is fitted. Although I've seen a tool (used on tv) that can actually cut a strip off the bottom of the skirting on the wall. You then slide the timber\tiles under the skirting.

You specifically said carpet though. Professional carpet fitters have no problem getting a perfect edge when butted against the skirting.

From what I've seen, Diyers do a better job fitting anything other than carpet. Any DIY carpet fitting job I've seen was a mess.

sinnerboy

soldsold wrote: »

How do you fit laminate or wood flooring any other way if the skirting touches the ground?Steve

Fit a slip bead over

FergusD

Is this not a case that there's an air-tightness issue where the wall meets the floor and once you accept that you can deal with it in several ways? The details say:

"Seal between wall and floor air barrier with a flexible sealant OR seal gap between skirting board and floor with a flexible sealant"

So it isn't essential to seal the skirting, just to address the underlying issue so to speak. I hate slip beads, but that's just a personal preference!

Fergus.

soldsold

FergusD wrote: »

I hate slip beads

I second that. UGly.

Carpet laying in a room that is narrow enough just to use one roll with no joints is actually a simple DIY job if using a decent carpet that is thick enough that it doesnt need underlay, Spray glue on the carpet as you roll it out (instead of tacking down and stretching). My carpet is down a few years now and is still perfectly flat and smart looking.

fuchia

Hi Guys,

Back to the origional question.

I have 9"*2" joists on my flat roof. There is a tapered lat on top of the joists to give the flat roof a fall. I intend to put two 4" layers of rigid insulation between the joists and then staple the airtight membrain to the underside of the joists. This will leave a 50mm air gap on top of the insulation under the plywood. The airtight rep called out to have a look. He thought this was fine aslong as I used plaster slabs without the foil backing.

Has anyone any thoughts on this?

Regards,

Fuchia.