Attic ventilation baffles

Up Donegal

What's the best type of attic ventilation baffles to use and what's the easiest way to fit them from the inside?

disposableFish

Kind of curious myself.

I remember seeing them in an american video but don't think they're used here and haven't been able to find a comparable product here. (best I could find was buying them from the US on ebay).

For anyone wondering...
They're bits of plastic that provide a path for airflow but still allow you to shove insulation right into the corner of the rafter/joist.

Calahonda52

Up Donegal wrote: »

What's the best type of attic ventilation baffles to use and what's the easiest way to fit them from the inside?

.
Close to impossible. period
.
because they need to be sealed airtight against the wall plate and along the rafters

disposableFish

Calahonda52 wrote: »

.
Close to impossible. period
.
because they need to be sealed airtight against the wall plate and along the rafters

Some are definitely designed to go on after.

...but I don't get the point about airtightness? It shouldn't really matter where they're going*, indeed it doesn't look like they're designed to be airtight.

Are we thinking about the same thing/use?

*ok, so it will on the topplate to some extent. I don't see it being that hard and if you wanted to be sure then you could put a quick bead of expanding foam around it. Beside, what's the alternative? Seems like a lot of places - especially with blown insulation - there just wouldn't be any insulation that far into the eaves anyway(probably none on the top plate at all), so you'd still be doing much better.

Calahonda52

Ventilation baffles are used in three applications:
.
1: before spray foaming: I won't discuss that option here.
2. with eaves level ventilation strips: as 1
.
3: to stop air from ventilated soffits passing through the insulation laid on the ceiling.
this becomes a real problem when additional insulation is added and it presses out against the roofing felt.
The VBs in this case are L shaped, with wings on the long part of the L and they are made airtight to the wall-plate and to the rafters, using the wings, creating a gap between the roofing felt and the baffle so as the air passes up into the cold roof space .

XF is not airtight.
As to easy to do internally, I have been that soldier doing that work, just try it in a cut timber roof, and then for extra marks in a hipped cut timber roof

listermint

disposableFish wrote: »

Kind of curious myself.

I remember seeing them in an american video but don't think they're used here and haven't been able to find a comparable product here. (best I could find was buying them from the US on ebay).

For anyone wondering...
They're bits of plastic that provide a path for airflow but still allow you to shove insulation right into the corner of the rafter/joist.

This stuff looks cool.

.but doesn't appear to cover 50% of the rafter timber. 50% of the timber should be getting that airflow. Not 30% as it appears in the image

Calibos

Looks at least 50% to me. The channels are V shaped and wider right under the Plywood roof deck if thats the correct terminology. Im on an ipad so could quickly zoom the image.

listermint

Calibos wrote: »

Looks at least 50% to me. The channels are V shaped and wider right under the Plywood roof deck if thats the correct terminology. Im on an ipad so could quickly zoom the image.

'At least' 50% .........Your 50% must be different to mine...

(attached)

when we talk about 50% minimum ventilation we are talking about the bit covered by the baffle. not the bit exposed to the inside of the attic space.

Calibos

listermint wrote: »

'At least' 50% .........Your 50% must be different to mine...

(attached)

when we talk about 50% minimum ventilation we are talking about the bit covered by the baffle. not the bit exposed to the inside of the attic space.

??

50mm depth of a ventilation gap. Looks about right to me if that rafter is 150-200mm deep.

I thought the 50% you were talking about was what percentage of the horizontal dimension of the plywood roofdeck was ventilated

listermint

Calibos wrote: »

??

50mm depth of a ventilation gap. Looks about right to me if that rafter is 150-200mm deep.

I thought the 50% you were talking about was what percentage of the horizontal dimension of the plywood roofdeck was ventilated

The 50% is the width of the rafter and no that thing is covering about 30% or less.

Dr_Colossus

Calahonda52 wrote: »

Ventilation baffles are used in three applications:
.
1: before spray foaming: I won't discuss that option here.
2. with eaves level ventilation strips: as 1
.
3: to stop air from ventilated soffits passing through the insulation laid on the ceiling.
this becomes a real problem when additional insulation is added and it presses out against the roofing felt.
The VBs in this case are L shaped, with wings on the long part of the L and they are made airtight to the wall-plate and to the rafters, using the wings, creating a gap between the roofing felt and the baffle so as the air passes up into the cold roof space .

XF is not airtight.
As to easy to do internally, I have been that soldier doing that work, just try it in a cut timber roof, and then for extra marks in a hipped cut timber roof

Resurrecting this older thread as it's something that's been on the long finger a while. In the case of 3 above I realise it's impossible to seal against the wall plate and rafters but bar taking the roof off any decent product available locally to help?

I have a hipped roof with only 100x35 mm joists and rafters in the attic so there's only 100mm fiberglass insulation between the joists that's barely reaching the wall plate if at all in most places. I'm planning on topping that up to 400mm but there's only a soffit vent along every 3rd or 4th rafter so don't want to impede the existing airflow.

I've seen the roll out rafter vent tray on Goodwins/McMahons and while the picture on Goodwins looks promising the product itself I believe is designed for inclusion as part of the roof build. Also while economical it looks light gauge so not sure how effective it would be from keeping additional insulation away from the felt. How about running it along the inside of the rafters just to prevent additional insulation from pushing it's way out to the felt and blocking airflow.
https://www.goodwins.ie/products/roll-out-rafter-vent-tray-300-mm-x-6mtr.html
https://www.mcmahons.ie/roll-out-underlay-rafter-support-tray

I've also come across the below available in Cherry Orchard which looks promising and more like that in the OP but very expensive at €4.15 a pop. However no details as to widths/depths etc so wondering how effective they would be.
https://www.roofnstop.ie/eaves-ventilation/GVRV635.html

I might call into them on Sat morning for a look as I've to go that direction to McMahons anyway for 35mm timber that I can't get in my usual Goodwins in anything over 75mm. Not sure why 1 1/2" timber is so difficult to source in comparison to 1" or 2".

Dr_Colossus

Dr_Colossus wrote: »

I've also come across the below available in Cherry Orchard which looks promising and more like that in the OP but very expensive at €4.15 a pop. However no details as to widths/depths etc so wondering how effective they would be.
https://www.roofnstop.ie/eaves-ventilation/GVRV635.html

I might call into them on Sat morning for a look

To update, called into the above this morning but they didn't have any stock to view. They have some pre-existing orders to fulfill and having difficulty sourcing from their supplier but hope to have an update on availability in a week or two.

listermint

Dr_Colossus wrote: »

To update, called into the above this morning but they didn't have any stock to view. They have some pre-existing orders to fulfill and having difficulty sourcing from their supplier but hope to have an update on availability in a week or two.

https://www.ebay.co.uk/itm/263769396154

This does the same job. I wouldn't worry to much about having something that bends it would mean more cutting between joists and a whole lot of faff.

Lifting first tow of tiles and rolling this out would be easier and cheaper.

Dr Bolouswki

How does the air go from the soffit to the apex of the roof? Is it that gravity keeps the insulation away from the interior roofing felt thus leaving a channel for the air to run?

Calahonda52

listermint wrote: »

https://www.ebay.co.uk/itm/263769396154

This does the same job. I wouldn't worry to much about having something that bends it would mean more cutting between joists and a whole lot of faff.

Lifting first tow of tiles and rolling this out would be easier and cheaper.

the stuff in the link is for full length eaves level ventilation and is not a solution where the soffits are ventilated

listermint

Calahonda52 wrote: »

the stuff in the link is for full length eaves level ventilation and is not a solution where the soffits are ventilated

Your baffle merely bends down around the front of laid insulation. The stuff I showed allows the same airflow up beyond the insulation without bending around the front.

It's purpose is to keep a designed gap between the roof felt and the insulation that's pushed up against it. Its sole role is to stop pushed insulation from closing the gap entirely stopping airflow.

Is it your assertion that just because yours has plastic bent around the front that the one I linked is not suitable or what makes it not suitable for ventilated soffits.

listermint

Dr Bolouswki wrote: »

How does the air go from the soffit to the apex of the roof? Is it that gravity keeps the insulation away from the interior roofing felt thus leaving a channel for the air to run?

You should not install insulation the full width of the rafter. There should be 50 percent of your rafter free for airflow. So you would either install insulation of a certain thickness level with the front inside facing of the rafter or install rafter cards to stop insulation being pushed back fully to the felt.

Also the ridge line detail should be taken into account you need the air to flow out the top of your ridge line too.

Calibos

You are going to have to re-clarify what 50% you are talking about because I’m still not sure what you are talking about and still wondering are you confusing it with the 50mm ventilation gap between an impermeable roof felt under the slates and insulation. ie 50mm of the depth of the rafter Behind the felt must not have insulation to insure attic ventilation and the breathability/drying of condensation of the rafters.


When you say ‘50% of the width’ do you mean a ventilation channel behind the insulation between rafters must span at least half the distance between one rafter and the next one either side. Surely a vent card that doesnt span the whole width, while still OK for attic ventilation doesn't actually expose the rafter to the airflow? So how is condensation dried out?

Calahonda52

listermint wrote: »

You should not install insulation the full width of the rafter. There should be 50 percent of your rafter free for airflow. So you would either install insulation of a certain thickness level with the front inside facing of the rafter or install rafter cards to stop insulation being pushed back fully to the felt.

Also the ridge line detail should be taken into account you need the air to flow out the top of your ridge line too.

The regs only require ridge ventilation when the span is > 10 meters.

listermint

Calahonda52 wrote: »

The regs only require ridge ventilation when the san is > 10 meters.

I'd want to be better than regs if I'm insulating the rafter space. Regs are minimum standards

cruizer101

Interested in doing this myself, came across these, available here



They seem like a good option for providing ventilation to the attic space, curious what others think

listermint

Looks good id still be looking to seal the bottom edge with tape.