Breathable felt colour change, concern?

[Ruggers]

I had a roof extension added 10 years and the side which is exposed most to the elements, the breathable membrane has some dark patches inbetween each slate lat. The outside is slated, large at the bottom getting smaller to the top.

Is this anything to be concerned about?

 

[Alastairreid]

Its condensation, increase ventilation to your roof space.

 

[JohnD]

probably worst on frosty mornings?

Looks like your loft insulation is incorrectly pushed into the eaves, blocking ventilation.

see also
https://www.diynot.com/diy/threads/condensation-in-loft-answers.160032/

 

[Ruggers]

By a slate vent or more soffit vents?

 

[JohnD]

have a look right in the eaves, see if they are open or if there is a soffit.

My house has open eaves, but you can drill holes into a soffit (and add insect gauze)

If you can open ventilation on each side and each end, any wind or breeze will create a through draught. You may need to experiment until you have enough. You will have to draw back or trim the insulation by a few inches, it will probably still cover the inner leaf of bricks and the cavity. It will be much less work than adding vent slates or a ridge vent. Slates fit very close so I don't think it will help to open the membrane overlaps.

It does look like your insulation is pushed too far. There should be a gap.

 

[JohnD]

rockwool say leave 25mm all along the eaves, but due to method of roof construction, my gap is bigger than that (see 3 minutes in)

I'd use a much bigger crawl board than they show.

 

[Ruggers]

probably worst on frosty mornings?

Looks like your loft insulation is incorrectly pushed into the eaves, blocking ventilation.

see also
https://www.diynot.com/diy/threads/condensation-in-loft-answers.160032/

I've not actually checked it to the touch on frosty mornings but will do. It's on the hip side of a 2 storey extension. Theres 3no. 70mm soffit vents to each face of a semi detached house. So 9 soffit vents in total. The old part of the house has bitumen type felt but is fine. The insulation does go too far into the soffit on the new extension so i can cut this back. If need be i could add more soffit vents too. I will real seal the rubber on the loft hatch and double check the bathroom extractor fan ducting is secure to the fan, It's mounted to the roof outlet securely when I checked.

The soffits sit around 250mm lower than the inner wall plate height.

Does there need to be higher up ventilation if the soffits are low down to let any moisture that does enter escape?
What distance should be left from the end of the

 

[JohnD]

if you have ventilation both sides and both ends, I'd expect airflow to be enough.

if actual steam is entering from a bathroom or wet washing is being hung in the house, there could be enough water vapour to need ridge vents, but a better solution would be to correct the source.

I've cut my insulation about four inches clear at the eaves, on a slope so you can look down it but it rests on the wall. seems fine to me. This means it doesn't extend beyond the inside face of the rafters, leaving an open channel between them.

 

[^woody^]

It mould from condensation.

The membrane is way too tight. You would benefit from opening the laps with some polystyrene if possible without stretching it too much

 

[Ruggers]

It mould from condensation.

The membrane is way too tight. You would benefit from opening the laps with some polystyrene if possible without stretching it too much

The roofer who fitted it was also one who works alongside a local building company who won lots of awards. Won't be using him again if it's fitted too tight. I seen some of them cheap plastic things that slide down the laps of the membrane so i will buy a couple of packs, add a couple more soffit vents and this weekend I'll remove the insulation thats pushed too far into the eaves possibly blocking them to prevent further mould. I've resealed the loft hatch too.

Even if i resolve it all, it's probably not going to look good to a valuer when i come to sell being white membrane.

 

[Ruggers]

if you have ventilation both sides and both ends, I'd expect airflow to be enough.

if actual steam is entering from a bathroom or wet washing is being hung in the house, there could be enough water vapour to need ridge vents, but a better solution would be to correct the source.

I've cut my insulation about four inches clear at the eaves, on a slope so you can look down it but it rests on the wall. seems fine to me. This means it doesn't extend beyond the inside face of the rafters, leaving an open channel between them.

I'm sure I seen someone fitting new roof trusses running a board around the inside of the rafters where they attach to the ceiling joists to prevent any isulation being pushed into the eaves and maintaining the air gap for the thickness of the rafters. Not sure if this is over kill or good idea.

 

[JohnD]

seems like a time-saving technique.