Overspill into flat roofs

-
White wool overflowing under flat roof
I managed to get my endoscope under the flat roof and found overspill of insulation which is visible in the distance int he photo.
This indicates that the cavity isn't closed at the top which is a requirement of cavity wall insulation though not much is mentioned in CIGA's guides about how you would inspect the top of a flat roof.
It makes me worried that the other flat roofs segments of the house are filled with this crap as well.

I have already established that the installers were incompetent and didn't check the wall on the gable end of the pitched roof as it overflowed into the attic but this was much harder to spot.

Overflowing CWI into a flat roof space can cause problems. Apart from forming patchy insulation which can lead to cold areas, in this case it fills the whole height of roof space between the joist and blocks of ventilation.
impedes ventilation and stops areas of timbers from shedding moisture adequately which leads to rot.
The other problem is that depending on how the walls are arranged it may overflow right up to the fascia board on the external wall where it is far more likely to get wet and as demonstrated, this white wool wicks water like cotton wool.

 Some low resolution thermal images looking up at the ceiling concurs with the limited visual inspection and gives an idea of the extent of the insulation overflow which at one point covers half the roof. The temperature difference is almost 2 degrees - so it certainly works unintentionally as patchy roof insulation.

Looking up a the inner corner of the flat roof ceiling 

Ceiling above corner window showing part of a big patch of insulation overspill.

If you are going to have insulation in flat roof the building regulations recommend a 'warm deck' which involves building insulation on top of the existing flat boards on the roof in a similar way to external insulation panels for walls.
As I understand it, you strip the roof down to the plywood/OSB, put a vapour barrier then 120ml or so insulation boards, then screw down another layer of plywood and apply the roof covering e.g felt, rubber or fibreglass as usual.
This arrangement allows the sub roof space to ventilate, and avoids a cold ceiling surface in the room.

An alternative 'cold deck' is permitted which involves  opening the roof up and placing insulation between the joists but there must also be a 50ml gap between the insulation and the roof substrate. 

Blown insulation in the roof-space wether intentional or accidental is not acceptable.




Comments

Post a Comment

Popular posts from this blog

The controversy over Cavity Wall Insulation 'topups'

-
Image
In this article I talk about the practice and problems of topping up insulation when voids are discovered, why it is being done and the potential violations of building regulations. I can only put forwards what I have understood from public documents and personal correspondence  So I welcome corrections or clarifications from the industry on this important issue for home owners and will happily update this post to reflect any inaccurate statements. We know that 100s of topups are done every year.   From what I can gather : If the BBA have not approved these topups then the relevant local authority building control should have been notified prior to topping up as an 'off licence' use of the product.  It is not clear that the correct procedures are being followed in all cases. Background :Voids are common A void is simply an area cavity between the walls which is missing insulation.  If a void is large enough then the insulation will not be compliant with the meter square
Read more

Discrepancies between Internal and external DPC (damp proof course)

-
Image
In a cavity wall construction, one would expect that the damp proof membrane to be at the same level on both walls. It turns out this is not always the case and my house is a good example where the internal wall's DPC is more than a brick lower than the external wall DPC. I didn't even think to check this before reading the CIGA Technical note 14 . This clearly states that if the distance between DPC and ground level is within a brick (as was the case with my property at time of install) then 'numerous other factors' must be assessed before declaring the dwelling as being suitable for CWI. CIGA  Technical note 14 . One of the factors is the relative level of the inner and outer leaf DPC. This is exactly what I found in my property. Ive used a floorboard to show the position of the internal floor. The DPC is clearly a brick below the floorboard and less than brick above the block paving. External leaf DPC is 1 brick below the floor level.
Read more

CWI, Impermeable masonry paint, hard cement and breathability

-
Image
Waterproof or let's call it plastic masonry paint made with silicone or acrylic sounds like a fantastic idea to keep that pesky rain away from the wall. Unfortunately it can easily cause the opposite in terms of moisture management and inflict devastating damage to old solid walls which were originally made with a breathable building envelope. This article serves as a discussion to highlight some of the unexpected problems which show up in the real world verses the limited testing of the BBA certificates and I welcome discussion from anyone interested in this subject. For a good 'primer' on the problems associated with plastic paint in solid walls, Peter Ward from Heritage House has a number of videos of detailing the sacrilege caused by often well meaning tradesmen applying these aggressively marketed products. I recommend watching all his videos especially if you are having any sort of damp problems so that you can avoid the multimillion pound interventions sold by 
Read more