Over Fascia Vents - Too Much Airflow in loft?

[Matte496]

Hi Everyone,

We have recently had a new slate roof installed and, at our request, we asked for over fascia vents to be fitted around the entire perimeter of our four-sided hipped roof (which measures about 13m wide by 10m deep).

We asked for this form of ventilation as we thought it was the most aesthetically pleasing option, as well as reading that continuous over fascia ventilation provides a good level of airflow. The vents essentially provide a 10mm opening above the fascia board that continues around the entire perimeter of the house at eaves level.

Aftrr a short while we started to realise that the vents provided a huge amount of ventilation - so much so that even in moderate winds the attic / loft becomes something akin to a wind tunnel. Whilst I appreciate ventilation in a loft is by no means a bad thing, this takes it to another level and the noise of the wind in the loft can become audible from inside the upstairs of our house even if it doesn’t appear particularly all that windy outside!
Has anyone else encountered this issue with over fascia ventilation? The only thing I can think of is that soffit vents are pointed downwards and are therefore protected somewhat against a direct wind, whereas fascia vents take a direct hit!

Can anyone think of any potential resolution? What would be the best and / or easiest way to dampen the air intake so that it is not quite so excessive?

Many thanks in advance for any help offered.

Matt

 

[motorbiking]

Loft roll over the entrance points will reduce some of the flow.

 

[Matte496]

Thanks for the quick reply!

so, if I get some 200mm loft insulation roll and wedge it right into the eaves where the vents are this should do the trick? Is it likely to stay in place?

 

[catlad]

If you put some strips of ply, maybe 300mm wide, across the bottom of your rafters, you will then have a series of letterbox type openings, which you can baffle with timber to reduce the amount of air flow.

 

[^woody^]

Did you ventilate the ridge too?

 

[Matte496]

No, there is no ridge ventilation, just the fascia vents coupled with the breathable membrane?

 

[Matte496]

Also, we have a lead ridge so not sure if a ridge vent is an option.

We were told by our roofing contractor that a 10mm continuous vent at eaves level was sufficient to meet new building regulations?

Would a ridge vent not just increase the airflow travelling through the roof?

Thanks

 

[datarebal]

was the original roof slate?

 

[Matte496]

Yes - it has always been a slate roof… to be honest we have built the house from scratch so it is a totally new design!

 

[^woody^]

Ventilation should be from eaves to ridge. This ensures that no humid air hovers around in the upper part of the roof. I'd also suggest that that could have evened out the air pressure, preventing the extreme air movement you are experiencing - which is not at all typical.

But if there is breathable membrane, you could most likely block up the eaves vents - and without them venting at the top of the ridge, they are probably not doing much in any case.

Is the roof membrane sagging? That too is a typical requirement, and again that could help deal with the excessive air movement at the eaves by evening out the air pressure

 

[Matte496]

Thanks a lot for your help with this.

Our roof ridge covering is of the lead broom-handle style so I’m pretty sure wouldn’t be compatible with a ridge vent?

Do you think a few slate vents close to the ridge would do an adequate job in terms of providing exhaust venting?


Thanks.

 

[^woody^]

Do you think a few slate vents close to the ridge would do an adequate job in terms of providing exhaust venting?
.

I wouldn't bother doing that as you won't know the results after all the work. You could experiment by opening the membrane laps with a wedge of polystyrene or handful of quilt insulation.

TBH, I'll just shove some quilt insulation down at the eaves to block or at least reduce the passage of air. If you tuft the quilt it will act as a baffle and still let air through. Then monitor for excessive condensation build up - 'excessive' though as some condensation is normal.

 

[Matte496]

Woody,

Thaks a lot for the advice.

Quick question - how do I tell if the membrane used is actually of the breathable kind?

I am sure the roofing contractor said he was using a breathable membrane called Tyvek, but apart from taking his word for it I have no idea!

Thanks,
Matt

 

[datarebal]

It looks like a breathable underlay in the pictures .some people refer to breathable underlay as Tyvek... It's a brand name not type .