Felt Lap vents - any good??

[NickK]

Hi,

 

Has anyone got experience with these?? https://www.amazon.co.uk/Vents-Prevents-Condensation-Attic-Ventilation/dp/B00M97O5YY/ref=mp_s_a_1_1?dchild=1&keywords=felt+lap+vents&qid=1609955428&sprefix=felt+la&sr=8-1
 

We have quite a bit of condensation in our loft and soffit vents are clearly not enough. Are these any good?

 

Thanks

[PeterW]

Short lengths of overflow pipe work just as well and much cheaper !

[nod]

I’ve just fitted ten at my daughters 

Manthorope I think 

Time will tell  if they have done the job 

As Peter has already said A bit of overflow pipe would have done exactly the same job 

 

[NickK]

@PeterW do you just a tiny overflow pipe for loft water tank for example?

[epsilonGreedy]

1 hour ago, NickK said:

We have quite a bit of condensation in our loft and soffit vents are clearly not enough. Are these any good?

 

 

Do you have the type of soffit vents that create an air channel between the soffit and up above the insulation roll level?

[NickK]

I do but at both front and back of the house and it isn’t covered insulation rolls...I guess simply not enough to for this time of the year???

[Temp]

Interesting to calculate how many of the round eaves vents you need to meet the recommendations in regs.

 

If the insulation is at joist level they recommend the equivalent of a 10mm wide slot so that's 10,000 sqmm per meter. Typical round vent has a free area or just over 2000 sqmm so you need 5 per meter or say 2 per rafter bay.

 

If the insulation is between and under rafters its a 25mm slot, 25000 sqmm per meter or 12 round vents per meter. Something like 5 per rafter bay.

[PeterW]

5 hours ago, NickK said:

@PeterW do you just a tiny overflow pipe for loft water tank for example?

Yep - couple of bits every other bay both sides of the roof. Your vents aren’t that big, needs a low flow not a gale 

[tonyshouse]

I sometimes have pushed off cuts of pipe in the lap to increase ventilation -  free and no downside though I worry about bats, bees and wasps using them 

[MikeGrahamT21]

I used offcuts of PIR/EPS, cut into wedges, does the job

[NickK]

Thank you everyone. I’ll have a go later today. 

[NickK]

@PeterW Just wanted to report and say thank you. Little over 3 days in and condensation is almost gone after installing overflow pipe cut-offs. Top job.

[Jilly]

On 06/01/2021 at 17:57, PeterW said:

Short lengths of overflow pipe work just as well and much cheaper !

Sorry to be thick but could you draw what you mean, please? I think this might help me too but I can't visualise how..

[Gav_P]

1 hour ago, Jilly said:

Sorry to be thick but could you draw what you mean, please? I think this might help me too but I can't visualise how..

I’m guessing a bit like this

from a quick google search

[Jilly]

Ahh, OK. Thank you. I'm worried about hidden condensation in the vaulted ceiling

[PeterW]

21 minutes ago, Jilly said:

Ahh, OK. Thank you. I'm worried about hidden condensation in the vaulted ceiling

Can’t use it for that. You need to use a proper breather membrane and a vapour barrier below the insulation. 

[Jilly]

Mmm, I need to do more research, I'll do a separate post to explain.