Fitting soffit vents.

amfisted · 23 Jul 2017

After a couple of months of dithering, I'm just about to drill and install gable vents to ventilate the roof space of our bungalow. Its boiling hot in summer up there and dripping with condensation in winter.

I've had advice about gable vents on this forum already, but have been doing some further reading prior to fitting and its been suggested that I fit round vents to the soffits below the roofline, the soffits being the closed plastic version, in order to draw cooler air from down below to replace the hot air which hopefully be expelled from the gable vents above.

Does that sound like a sensible arrangement? Is it OK to fit plastic soffit vents in a UPVC soffit? I only ask because almost all the advice I've found online talks about fitting round soffit vents in wooden or plywood soffits, which makes me wonder whether they're not designed to be fitted in plastic soffits.

Thanks in advance.

KenGMac · 23 Jul 2017

amfisted, good evening.

Retro-fitting Circular vents into a PVC Soffit? I do not think that this is a good Idea? Why? because.

1/. PVC will not be easy to use a circular hole cutter in to, the PVC will buckle deform and possibly splinter? in short because the PVC is a hollow structure and not supported between the fixing noggins, trying to cut a clean circular hole will be to say the least "Problematic?"

2/. The proposed circular vents are held in to place by in effect Friction the hole and the vent sizing being crucial in that they must be a tight fit, the vents will work in a "Solid" material such as Ply or timber or indeed the DREADED Asbestos where a hole can be cut with precision, but? a hollow Plastic will not work?

Sorry to rain on you, but? I really think you need to try another solution?

Ken.

chappers · 23 Jul 2017

bit more work but you could drop the soffit out and replace with ventilated

amfisted · 24 Jul 2017

Not sure I'd want to go to that much trouble and expense just to introduce a bit of air movement into the loft, to be honest. I'm not short of time, but I'm looking for a quick fix rather than what (to me) would be a significant project.

I went up into the loft yesterday to see whether the edges are clear, and they've fitted insulation right up to the inner faces of the soffits. So I'll have to roll that back for the vents to have any effect.

amfisted · 24 Jul 2017

KenGMac said:
amfisted, good evening.

Retro-fitting Circular vents into a PVC Soffit? I do not think that this is a good Idea? Why? because.

1/. PVC will not be easy to use a circular hole cutter in to, the PVC will buckle deform and possibly splinter? in short because the PVC is a hollow structure and not supported between the fixing noggins, trying to cut a clean circular hole will be to say the least "Problematic?"

2/. The proposed circular vents are held in to place by in effect Friction the hole and the vent sizing being crucial in that they must be a tight fit, the vents will work in a "Solid" material such as Ply or timber or indeed the DREADED Asbestos where a hole can be cut with precision, but? a hollow Plastic will not work?

Sorry to rain on you, but? I really think you need to try another solution?

Ken.

Thanks for that. I read Chappers reply before I read yours, Ken, and having seen your post I now understand now why he suggested fitting vented soffits as an alternative.

Would a brand new hole cutter applied very cautiously not have at least a fighting chance of cutting a clean hole? And if that does work, a bead of silicone around the edge of the vent to hold it in place?

amfisted · 24 Jul 2017

What about (yes, a bit fiddly) wedging sections of timber between the rafters from the inside so that they lay flat against the inside face of the soffits and support the UPVC as I cut into it, and into the timber? Might that work?

I was only counting on fitting about half a dozen vents in total.

Mind you, maybe not. The rafters are obviously at an angle, so it would be impossible to get the timber flat against the soffit; unless I screwed it from the inside, and there's no room to do that. Boo hoo.

Chappers, your solution is looking better by the moment.

amfisted · 24 Jul 2017

I've just spoken to the boss of a local firm that installs UPVC products, including doors, windows and soffits. He said that his guys retro fit vents in UPVC soffits on a regular basis, and if the right holesaw is used and sufficient care taken, it should be no problem.

So I'll locate the least conspicuous part of the soffit and give it a shot.

Tigercubrider · 24 Jul 2017

Buy a bit of upvc and practice?

amfisted · 24 Jul 2017

Tigercubrider said:
Buy a bit of upvc and practice?

Thats a very good idea. I'll visit said UPVC company and ask whether they have a piece knocking about so that I can practice destroying it.

chappers · 25 Jul 2017

Worth a test though as some definitely cuts better than others also really aggressive cutters can snag and that can cause it to crack or shatter.
Go steady and you should be fine . you could always replace a bit if it all goes tits up

Xtrailer · 25 Jul 2017

I've fitted these round vents exactly as you said you would like to do them. They fit without gluing or wedging as they have a lip on the top edge that will catch in position as long as you use the correct hole saw.

If your soffit material is of hollow construction I found it easier to drill the pilot hole and then cut the hole with the hole saw running in reverse (assuming it's good and sharp) running in reverse still cuts ok and doesn't result in the teeth trying to pull it through the thin sheets too quickly.

amfisted · 25 Jul 2017

Thanks again for all replies.

I've fitted the vents today, and had no trouble cutting the holes using an Erbauer pilot bit and 70mm hole saw from good ole Screwfix. It quickly became apparent that the plastic soffit has been installed against thick plywood, and that obviously helped to reduce vibration, but the job was much easier and stress free than I expected. I can already see light at the edges of the loft, and that's before rolling back the insulation which has been packed right up to the inner faces of the soffits.

One thing I did have to think about was positioning of the vents on the kitchen side, where in the wall below the soffits there's an extractor vent and balanced flue for the boiler. I made a point of avoiding putting the vents above these, because it struck me that there might be a risk of cooking fumes/ combustion gases being drawn into the loft space.

amfisted · 25 Jul 2017

Right...I've been up in the loft to clear the insulation away from the roof edges where the vents are. You can actually see daylight in the roof space now, though as yet I can't sense any air movement up there, even though today was a little windy. So I may have to supplement the soffit vents with gable vents after all.

Now looking to ensure the soffit vents continue to be effective by fitting something to keep the insulation from closing up those gaps again, and I found this: http://www.roofingvents.co.uk/eaves...MIi8COsoel1QIV7rvtCh0_hg4UEAQYBCABEgLdL_D_BwE

Would that be the right stuff to use in the circumstances?

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Fitting soffit vents.

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