Hi all

I am new to the forum, and am seeking some advice.

We renovated / extended a small bungalow and moved in last year, but are experiencing issues with condensation / mould in some rooms and now also condensation in the loft, but only down the valley sections of the roof.

Details of the property:

Single storey bungalow. 2 remaining original walls have been full filled with carbon coated polystyrene balls (65mm cavity). New walls are all double leaf with 100mm knauf slabs in between. Floor is beam and block with 100mm PIR.

Masterbedroom and Lounge have raised ceilings / skeilings and this section of the roof has been done as a "warm roof" with 100 PIR at rafter level, then some form of multi layer foil under the joists, with dupont airguard under that prior to the plasterboard. This is then segmented from the remainder of the house via wooden frame section in loft with 100mm PIR infill.

The remainder of the house is "cold roof", with 300mm Isover spacesaver glass wool (100mm within joist, 200mm over). No dupont airguard fitted to cold roof side. The loft hatch appears to have seals.

The whole roof is covered with TIL-R breather membrane.

Due to the layout of the roof, there is only a small section of eaves, approx 3m on the front and back of the property, as the remaining area is gable end - the house is "cross shaped" so we have 4 gable ends, one being in the warm room side, so cold roof as 3 gable ends and minimal eaves. There is no ridge tile venting.

From what I can see the eaves dont look blocked and I think there is some form of eaves tray / eaves vent - need to inspect more closely.

There are no soffit vents

3 x Wet rooms have MEV to roof tile vents via insulated 100mm ducting.

My thoughts are that:

1) There is too much moisture getting into the loft
2) Due to minimal eaves there is not enough cross venting to allow adequate ventilation even with a breather membrane.

My plans to rectify are:

1) Fit new IP65 downlighters to all rooms, in place of the currently fitted IP20 standard ones, and also apply foam around the canister to seal.

2) Seal any other minor holes foudn in ceiling with foam

3) Apply superfoil SFBA MP between the joists of the cold roof at plasterboard level and then tapping to inner sides of joist to provide a vapour / more air tight barrier, then relay 100mm glass wool over this between joists then the 200mm back across the joists.

4) Check the eaves in detail and potentially fit a 3 in one system to improve ventilation.

5)Consider further roof tile vents or get vented ridge tiles fitted to allow better ventilation

Would be useful to hear other people thoughts / views / experience on the above

John

... who fitted MEV? Have you checked ducts-to-vents joints yourself?

<blockquote><cite>Posted By: DarylP</cite>... who fitted MEV? Have you checked ducts-to-vents joints yourself?</blockquote>

Builders, but I have checked it. Ventilation is intermittent and on an overrun timer - 20 mins after switching light off.

<blockquote><cite>Posted By: djh</cite>Is the MEV continuous or intermittent or humidity controlled etc? What other ventilation and heating is there in the house?

For the loft condensation I would concentrate on increasing ventilation and on making the ceiling airtight. Note that IP65 is a standard for resistance to water damage, not for airtightness. I believe it is possible to buy airtight back boxes for downlights, although like Tony I don't use downlights. I like his clay flowerpot idea, though I am a believer in good quality tapes (e.g. Siga or Pro Clima) which would simplify their use.

Check for ceiling holes around junctions with walls, especially external walls. Pay special attention to areas around joist supports.

I'm a bit confused about the ventilation at the eaves. If there are no soffit vents, how does the air actually get to/from the outside?</blockquote>

I understand re the IP65 but at that level it is dust tight, so I figured they would be much more airtight than the ones I currently have in the roof. Aurora do have some mPro models that have an airtight standard mentioned, so could consider those.

I could always silicone around the front of the cans where they meet the ceiling or use a small amount of foam around the gap.

With regards to the eaves I will take a close look this weekend. I had a look via the loft side and there appears to be some form of channeled black plastic under the membrane, so there could be an over fascia vent in place. I will report back once Ive checked.

Fitting louvres to the back gable will be very difficult as the conservatory spans its entire length, so I have no way of getting to the outer wall without mass expense of a special scaffold over the conservatory. Side gable wouldnt be an issue. I assume I would need vents with 300mm wall sleeves?

Ive got 4 x spare roof tile vents so I could put those in near ridge and low level on each side of the front and back gable to increase ventilation?, then louvres to the side gable?

The mould in the rooms is on the window reveals, bottom corner. I think I have sourced the issue with than in so far that the windows have not been silicone in well and dont have any foam around them, so I am going to sort that out for all the windows, as that is clearly creating cold spots were moisture is then foaming.

Bit of a knightmare and clearly things not done correctly by the builder.

<blockquote><cite>Posted By: gyrogear</cite><blockquote><cite>Posted By: johnmwingnut</cite>We (...) are experiencing issues with condensation / mould in some rooms and now also condensation in the loft, but only down the valley sections of the roof.

Masterbedroom and Lounge have raised ceilings / skeilings and this section of the roof has been done as a "warm roof" with 100 PIR at rafter level, then some form of multi layer foil under the joists, with dupont airguard under that prior to the plasterboard.</blockquote>

Can you confirm no condensation / mould in "warm-roof" area ?

I understand that your main problem seems to be the loft, but I am nonetheless curious regarding your "warm roof" buildup which to me sounds somewhat confused: normally with a warm roof, all of the insulation is ABOVE the roof structure, airtightness being provided by (for example...) the plasterboard skeiling... I cannot therefore see the point of the MLC stuff or for that matter the Airguard...

Your warm roof is then either ventilated or unventilated, depending on how it was designed.

In this case I would think twice before ventilating (or unventilating ) it. As Tony said, wall vents in gable if necessary.

gg</blockquote>

There is no condensation in the "warm" side as went in a took a look.
All I can say is that there is 100mm PIR at rafter level with aluminium tape on it between rafter and PIR board with a gap of 10mm between PIR and breather membrane

Then on the skeiling bit, there is multifoil under the joist then airguard then the plasterboard. So yes, not a conventional warm roof build, so they have put insulation at both levels? Not sure why.
This section is separated from the cold roof side.

The issue with the cold loft is condensation just on the valleys, clearly the coldest point as breather membrane touches the GRP valley and is cold so condeses the moisture on there and saturates the membrane and then drips off.

I have just taken a look at my eaves and all the way around the property there is an overfascia vent. Looks like Redland rapid vent https://www.youtube.com/watch?v=mn4bSqiDlVE, so this should be providing decent ventilation to the roof.

So the "warm" side is also ventilated

<blockquote><cite>Posted By: gyrogear</cite><blockquote><cite>Posted By: johnmwingnut</cite>breather membrane touches the GRP valley and is cold so condeses the moisture on there and saturates the membrane and then drips off</blockquote>

Hiya,

Thanks for the extra insight.

I'm not a roofer, but IMO the condensation should Run Down the breather membrane, to gutter, and not saturate it.

This implies that the breather membrane be tight (as the proverbial drum) and sufficiently spaced from structure above and below it, while providing unimpeded runoff to condensation (and indeed stormwater that gets through the roof covering...). A reading of the manufacturer's installation instructions (if retrospectively available...) would soon sort this one out.

It looks to me like a roof inspection is on the cards, as ventilation per se will not solve the issue if it turns out to be the worst-case (water ingress) as described above...

gg</blockquote>

Well, I have had a rummage in the loft eaves and the one at the back is completely blocked with insulation.

I have pulled the majority out, however, the black plastic eaves roll that is supposed to create air channels is completely flattened due to being crushed and is therefore serving no use.

Looks like I am going to need to replace this with a more sturdy product or a retrofit product:

https://www.roofingsuperstore.co.uk/product/manthorpe-g435.html

Anyone got any suggestions as to the best way for me to do this? Eg should I remove the damaged eaves roll or just leave it in there and put a new more rigid version in, then refit the insulation back in again?

As the roof pitch is shallow, its quite difficult to get right to the edge of the roof,from the inside so even fitting the product in the link above is going to be tricky

John

Should be insect-mesh-screened tho

The redland kit comes with the over fascia vent, eaves tray and the ventilation roll, and thats basically whats up there currently - so maybe the over fascia vents have a mesh screen in them??

I have sorted one side out today. I removed the soffit board, pulled out all the insulation, fitted new 300mm of insulation and tucked down over the wall / into the cavity plate. Then used some left over coreline corrugated shed roofing, cut it to 700mm lengths and pushed in down over the insulation to the fascia board.

Lovely draft coming into the loft now. Will do the other eaves next weekend, as thats enough loft work for me this week.

Did find another problem. Where the lead is at the base of the valley, there has clearly been water leaking out from under it onto the timbers as they were very damp. Putting ones hand up underneath it is soaking wet, so clearly something not right there.

Might have to get someone out to redo all 4 valleys as that is where the issues are - should not be soaking wet under them!!

John

Well done it seems you are making good progress .

Bare in mind condensation to a large extent is caused by life style .
I am sure you know but try to
keep the house temperature as stable as possible if you can possibly keep it within a couple of degrees over the 24 hrs it will help no end .

Avoid drying clothes or washing indoors and if possible steam from cooking and boiling kettles it will go a long way towards eliminating condensation in the living area .
It seems you have identified the cold bridges already which are often difficult to eliminate easily.
Good luck

So I went back up into the loft last night, 3 days post fixing one side of eaves. I also rerouted one of the extractor fan duct runs so it was much shorter (basically fitted a new RTV) then have left the remaining RTV open as it is just below ridge level where all 4 valleys meet at the top.

The valleys are pretty much dry now and the loft is more noticeably "airy" so I think once the other eaves side is cleared and vented properly I should be all good.

I have ordered 2 additional RTV to fit at low level on the each central gable, the side away from the eaves I am fixing.

I have also ordered some new extractor fans for the wetrooms - have gone with Vent Axia Svara as it has lots of combustibility as to how the fan runs which for me is a good thing.

Kitchen has a recirculating extractor, so Im toying with the idea of leaving it as such and fitting another fan or potentially removing the recirculation kit and ducting it to the outside

John

Sounds great! And much less hassle than retrofitting vapour barrier :-)
Consider (single room?) MHRV for the kitchen (and or bathrooms) instead of extractor
Get some humidity displays in the kitchen and elsewhere to find the source of humidity (fresh concrete/people breathing/cooking) before doing anything expensive