Bad condensation on felt

[m4tth3wb]

Since moving in our build, I have noticed in the loft on the inside of the roof felt there is major condensation, so bad it's starting to drip.

 

The house is traditional brick and block and has 300mm loft insulation (insulation company said any more is pointless)

 

The house had nearly a year to dry out before moving in due to doing most the inside work ourselves in spare time.

 

We have core drilled about four 100mm holes on each gable end to get more air flow in there but the same thing is happening!

 

I've checked the seal on the loft hatch and even around the extraction fans and all seems fine.

 

What else could I do?

 

 

Thanks 

Edited January 3, 2017 by m4tth3wb

[Simplysimon]

do you have an overhanging eaves? if so i would recommend ventilating there and ridge ventilation. if that has already been done, has the insulation been placed over it

 

simon

[Declan52]

You need a breeze to be able to blow through one side collect the moisture and out the other so have a look to see if the insulation is touching the felt at the wall plate stopping the air getting in. A couple of vent tiles would be a quick fix if you can get onto the roof without killing yourself.

[m4tth3wb]

No eaves at all, it's just a fascia right against the brickwork.

 

It had to be like this to blend in with the old terraces houses on either side.

 

If the core drilled holes on either side aren't working then would that mean the vented tiles won't make any difference either?

[Declan52]

The condensation is rising and hitting the felt so if you have maybe 2 tiles at the bottom of the roof and 2 at the top front and back this should cure it. How many vents will depend on how wide the roof is. 

Can you look under the first row of tiles to see if the is a eaves strip vent. Should look like this. 

 

http://www.plasticdrainage.co.uk/1m-continuous-eves-vent-strip-10mm-8531.html

[daiking]

This is something I am keeping an eye on in my own new extension loft. There is condensation but as yet it is not dripping.

 

The existing roof was re-felted and tiled at the same time and is (still) noticeably draughty and apparently without the same problem. The new loft section is not draughty at all, neither it is properly sealed from the bedroom and bathroom beneath it so I will be approaching this first. It did not help to leave some metal crawl boards in that loft.

 

 

[joe90]

When building an extension for a customer I noticed loads of condensation on the old type felt and the customer asked me to look into it for them. Apparently when they got a mortgage the inspection threw this one up and a condition of eaves ventilation in the form of 3" round soffit vents should be fitted, they were and the condition was retracted ( but no inspection of condensation was carried out) On removing the felt and tiles the brickwork extended right up to the back of the felt so the vents had no effect at all. This may be the case elsewhere but difficult to determine in some cases.

[Ferdinand]

Round soffits are about £3.50 for a pack of 10 from Screwfix :-).

 

Ferdinand

[Simplysimon]

i'd still look at ridge vents, there will still be some air circulation due to the holes as well as the space heating up, appreciate not much these months!

as @Sensus says, roofing felt, was the correct one used, i'm presuming a type was specified. and i hope the holes have been covered with something to prevent birds getting in.

simon

[MrP]

Try these felt lap vents, they work wonders and is a cheap and easily installed solution. Spread them out evenly across the roof and at different levels to maximise cross flow. http://www.manthorpe.co.uk/Building/Products/Roof-Ventilation/Felt-Lap-Vent.html

[Gone West]

  On 04/01/2017 at 21:32, MrP said:

Try these felt lap vents, they work wonders and is a cheap and easily installed solution. Spread them out evenly across the roof and at different levels to maximise cross flow. http://www.manthorpe.co.uk/Building/Products/Roof-Ventilation/Felt-Lap-Vent.html

Expand  

 

+1 My son-in-law used similar devices on his roof and it solved the condensation problem.

[PeterW]

Didn't JSH have a similar issue and used short lengths of 22mm overflow pipe wedged into the joins..??

[daiking]

  On 05/01/2017 at 09:19, PeterW said:

Didn't JSH have a similar issue and used short lengths of 22mm overflow pipe wedged into the joins..??

Expand  

 

Considering my typical household waste products, I imagine that 4 pint milk bottles will supply me a steady stream of loft ventilators.

[Dudda]

  On 05/01/2017 at 09:36, daiking said:

 

Considering my typical household waste products, I imagine that 4 pint milk bottles will supply me a steady stream of loft ventilators.

Expand  

Not sure if it's on BuildHub or elsewhere but I saw photos of someone using pringle crisp cans with the bottom cut off to separate the fiberglass insulation which was touching the felt preventing ventilation.

[gravelld]

  On 05/01/2017 at 09:19, PeterW said:

Didn't JSH have a similar issue and used short lengths of 22mm overflow pipe wedged into the joins..??

Expand  

 

Yes, the horizontal overlaps of felt.

[Temp]

There is some guidance on the web regarding the size of vents needed. It's surprisingly large. Works out at several of those screwfix vents per rafter bay as I recall. Will try and look up the figures.

[Temp]

Guidance says vents equivalent to a 10mm wide slot the full length of the eaves. Here they suggest 70mm diameter vents on 160mm centers will achieve that..

 

https://www.discountbuildsupplies.co.uk/shopdisplayproducts.asp?id=1101&cat=Circular+Soffit+Vents+70mm+&gclid=Cj0KEQiAwMLDBRDCh_r9sMvQ_88BEiQA6zuAQ1-pKlkBU2AYlDmnG-fTX9ixkW8g3jqtd9xfcpq8LWYaAs5K8P8HAQ

[m4tth3wb]

Stuck some of those felt lap vents in and after a very windy day recently it all seemed to dry out.

 

Will keep an eye on it and check if it comes back when the frosty weather comes back, but so far so good!

 

 

Thanks