Roof tile vents

[JohnBishop]

Hi All,

  What are your thoughts about roof tile vents?

The roofers have installed 3 of those on the north side apparently to mitigate some extra humidity.

Does it mean I should put some extra insulation? I think I have currently about 300mm. What about insulating the space under the breathable membrane under the roof?

Best

[Redbeard]

"Does it mean I should put some extra insulation?"

 

No. Not if the insulation is, as I assume, on the ceiling of the room(s) below, and the vents are on the slope at the top of a cold void. There should be a howling gale up there anyway for water vapour control. As long as it does not infiltrate to the 'warm side' of the insulation, no problem. If you want to put more insulation in top up to 400 - 500mm, but make sure not to block eaves ventilation. You could staple some membrane at the 'point of the triangle' in the eaves to deflect ventilation air above the insulation.

[JohnBishop]

15 hours ago, Redbeard said:

"Does it mean I should put some extra insulation?"

 

No. Not if the insulation is, as I assume, on the ceiling of the room(s) below, and the vents are on the slope at the top of a cold void. There should be a howling gale up there anyway for water vapour control. As long as it does not infiltrate to the 'warm side' of the insulation, no problem. If you want to put more insulation in top up to 400 - 500mm, but make sure not to block eaves ventilation. You could staple some membrane at the 'point of the triangle' in the eaves to deflect ventilation air above the insulation.

can you elaborate about the membrane at the 'point of the triangle'? how is this done?

[Redbeard]

Yes! I do not have pics, I am afraid, as I am one of the world's worst photographers. Basically temporarily clear away the insulation from the eaves. Work out the vertical height (depth) of the insulation you want. cut a piece of breathable membrane which is a bit more than the length of the hypotenuse of that triangle. Lie uncomfortably on your front with your head nearly wedged in the eaves and a staple-gun in one hand and the breathable membrane in the other. Staple to the underside of the rafters tightly, so that as you push the increased-depth insulation up against the membrane the ventilation gap (the gap between the membrane and the underside of the roof covering) remains fully open. If there is a stub of wall to seal the membrane to at the 'bottom of the hypotenuse' then even better. This 'deflector' should allow you to insulate tightly and deeply without risk of getting air-flow between the layers of insulation or compromising the ventilation.

 

I am sure someone with skills in CAD could draw that up in a moment.

[JohnBishop]

On 04/04/2023 at 14:07, Redbeard said:

Yes! I do not have pics, I am afraid, as I am one of the world's worst photographers. Basically temporarily clear away the insulation from the eaves. Work out the vertical height (depth) of the insulation you want. cut a piece of breathable membrane which is a bit more than the length of the hypotenuse of that triangle. Lie uncomfortably on your front with your head nearly wedged in the eaves and a staple-gun in one hand and the breathable membrane in the other. Staple to the underside of the rafters tightly, so that as you push the increased-depth insulation up against the membrane the ventilation gap (the gap between the membrane and the underside of the roof covering) remains fully open. If there is a stub of wall to seal the membrane to at the 'bottom of the hypotenuse' then even better. This 'deflector' should allow you to insulate tightly and deeply without risk of getting air-flow between the layers of insulation or compromising the ventilation.

 

I am sure someone with skills in CAD could draw that up in a moment.

 

In my case this is how it looks in the loft.

 

 

The roof bends so I don't have access to the actual very corner and also was wondering if I should insulate sloping ceiling from the inside as I reckon this creates a thermal bridging.

[JohnBishop]

So to summirize my understanding is that I can increase the insulation but make sure I don't come too close to the breathable membrane. Leave a gap basically.
This is the old picture since then I have put another 100mm Knauf on top of the pink.

[SteamyTea]

On 04/04/2023 at 14:07, Redbeard said:

 

I am sure someone with skills in CAD could draw that up in a moment

Crayon aided design.

 

Like this?

 

[Redbeard]

Splendid, ST! Thank you.

 

The next step is Auto-Crayon-Aided-Design, where the crayon guides itself.🙂

 

@JohnBishop, ST has depicted my suggestion perfectly. However now I have seen your pictures you need this less than I thought (indeed perhaps not at all if your pics are representative of the situation over the whole eaves). The point of 'my' membrane is to ensure that you cannot block the vent gaps. AFAICS, if they are what I think they are, your black plastic formers do exactly that; if you push the insulation hard against them there still remains airflow. So, message to anyone in future with this issue, if you have nothing to stop the vent path being blocked then mine is a fair idea. If you have plastic formers or similar like @JohnBishop's, you probably don't need my suggestion.

[SteamyTea]

1 hour ago, Redbeard said:

Auto-Crayon-Aided-Design

Computer Reaction Aided Production will be next.

[JohnBishop]

7 hours ago, SteamyTea said:

Crayon aided design.

 

Like this?

 

 

Thanks for the drawing.
Ok so in my case it is a bit different but for the membrane part I think it does not matter, as long as I have the membrane in there then I reckon I can stuff as much Knauf insulation as I want.

My question was also about the red bit which to my understanding is not insulated and I would expect thermal bridging going on in these corners. This would require insulation done from the inside.

 

 

[SteamyTea]

28 minutes ago, JohnBishop said:

My question was also about the red bit which to my understanding is not insulated and I would expect thermal bridging going on in these corners. This would require insulation done from the inside.

Can't think why not.

Evan 25mm of PU or EXP would help.

May need to drill some ventilation holes, or pull the plasterboard off and get more thickness.

Get a multitool and you can trim it all easily.

[JohnBishop]

On 10/04/2023 at 16:24, SteamyTea said:

Can't think why not.

Evan 25mm of PU or EXP would help.

May need to drill some ventilation holes, or pull the plasterboard off and get more thickness.

Get a multitool and you can trim it all easily.

What about inserting some 25mm Celotex on the outside? There is some rubble at the end but the gap is about H 10cm and 35-37cm wide. I would cut to size and fit it in.
I suppose the thin plastic thingies are to maintain the ventilation.

 

[SteamyTea]

4 hours ago, JohnBishop said:

What about inserting some 25mm Celotex on the outside?

Bit hard to tell what is what without seeing the problem in the flesh.

As long as there is some ventilation that cannot bypass the insulation, and still does the job, you should be OK.

 

Is that a cable in the top picture?

[Dave Jones]

On 10/04/2023 at 15:50, JohnBishop said:

 

Thanks for the drawing.
Ok so in my case it is a bit different but for the membrane part I think it does not matter, as long as I have the membrane in there then I reckon I can stuff as much Knauf insulation as I want.

My question was also about the red bit which to my understanding is not insulated and I would expect thermal bridging going on in these corners. This would require insulation done from the inside.

 

 

 

we call that a cranked roof. Very common in plymouth! 

 

It's allways the first area black mould comes a visiting. 

 

25/50mm celotex on the crank ill help a lot, its tricky sliding it behind the tiles but worth the effort.

[JohnBishop]

3 hours ago, Dave Jones said:

 

we call that a cranked roof. Very common in plymouth! 

 

It's allways the first area black mould comes a visiting. 

 

25/50mm celotex on the crank ill help a lot, its tricky sliding it behind the tiles but worth the effort.

indeed a cranked roof. This one is in Notts.
I monitor the humidity and I have to say it's surprisingly dry in the house between 44-47% and I have not seen any mould yet but I am sure it is due to these always opened vents in each and every window - what I blocked only recently so I could expect some raise in humidity but it didn't yet.
I reckon there is some other draft coming from the doors and perhaps the ground floor fire stove also circulates the air. Or maybe it's because in the loft it is relatively drafty and dry because of these new vents OR both.

It looks like it will be tricky to fit Celotex in but this would provide a more consistent insulation of the ceiling. This should be addressed in the first place rather than adding more Knauf.
I already have like 3 generations of mineral glass wool (yellow, pink and more recent 170mm Knauf top up) in the loft, could be 400-500mm.

Since I have a proper vacuum cleaner I could remove all the dust in the loft and maybe replace the old mineral glass but this won't be a 1-day job.

Edited April 26, 2023 by JohnBishop

[JohnBishop]

5 hours ago, SteamyTea said:

Bit hard to tell what is what without seeing the problem in the flesh.

As long as there is some ventilation that cannot bypass the insulation, and still does the job, you should be OK.

 

Is that a cable in the top picture?

Yes, this is a 10mm cable I just put in for the shower.

[JohnBishop]

ok, I schedule this work for August - September time as I have other more important projects at the moment.

Is Celotex the best material to use on the crank?

[JohnBishop]

I think I order some 50mm Celotex over summer.
What is the best way to cut it to size without destroying the edges?

Edited June 14, 2023 by JohnBishop

[JohnBishop]

Hi again, I know it's October and I supposed to do it in August but this year summer has shifted to September/October.

On the picture above you can see there is a joist and I cannot fit the Celotex because the joist is protruding and the gap between the membrane and in some instances the joist is less than the thickness of my Celotex which is only 25mm. I don't want to push it as this can disturb the roof tiles.
What if I fit one or two layers of SuperFoil instead?