Ensuring vaulted ceiling won't get hidden condensation

[Snowbeetle]

On 12/01/2021 at 14:14, ProDave said:

Is the roof on yet?  What is above the membrane in the photo?

 

If roof not on why not fit external insulation above the rafters and make it into a warm roof (very much like my own)?

 

Then you have eaves vents and a ridge vent to vent the gap between the breathable membrane and the tiles, and are you really telling me it is possible for a bat to enter through the standard eaves vent profiles? (e.g the OV10 that I used)  If the bats can't get in the type of membrane wrt bats is not an issue.

The bats get under the roof tiles and shelter between the roof tiles and the roof membrane. If they get snaggled they slowly starve to death. So it isn't necessarily getting under the eaves where they come into contact with the roof membrane. We have one living there in our roof (barn conversion) and have to keep the bitumen roof felt for this reason. 

[Jilly]

This vents look lovely, they'd completely upstage the red clay tiles!

[Jilly]

Here's an image of the roof as it went on. It seems to be a dry ridge. They are clay tiles. 

 

You can see one of the bat tiles on the left. They actually look like vents. 

 

From my research I think I need to insulate the steel and then decide if it's going to go in or out of the thermal envelope. 

 

I also need to chose suitable tile vents for each rafter bay as it the 50 mm gap doesn't seem to communicate with the ridge ventilation.

I could also add lap vents in each layer of the bitumen, again within each bay.

 

There are two places made for potential roof lights, and these should be notched to allow air flow.

Does this sound right?

 

[dpmiller]

certainly a dry ridge, but can't tell if it's vented or not...

[Dave Jones]

looks like they have lapped the felt wrong as well. higher up should overlap the ones below not the other way round as water can get in.

[SimonD]

On 18/01/2021 at 10:41, Jilly said:

From my research I think I need to insulate the steel and then decide if it's going to go in or out of the thermal envelope. 

 

I also need to chose suitable tile vents for each rafter bay as it the 50 mm gap doesn't seem to communicate with the ridge ventilation.

I could also add lap vents in each layer of the bitumen, again within each bay.

 

From looking at your image from the inside of the roof it looks like the steel does sit inside the thermal envelope as the joists filled with pir rest on a ridge beam that rests on the steel.

 

Re the vents - do you have the detail drawings produced by your architect/technician for the roof? Even before your change from sheepswool to pir insulation and bitumen felt, there would have been a 50mm ventilation gap specified for the structure?

[Jilly]

On 18/01/2021 at 11:42, Dave Jones said:

looks like they have lapped the felt wrong as well. higher up should overlap the ones below not the other way round as water can get in.

I went to double check all the felt today and it is lapped correctly, it must be an optical illusion, I can see what you mean, I was worried. 

[Jilly]

31 minutes ago, SimonD said:

 

From looking at your image from the inside of the roof it looks like the steel does sit inside the thermal envelope as the joists filled with pir rest on a ridge beam that rests on the steel.

 

Re the vents - do you have the detail drawings produced by your architect/technician for the roof? Even before your change from sheepswool to pir insulation and bitumen felt, there would have been a 50mm ventilation gap specified for the structure?

Yes, a 50mm gap was specified.

Edited January 20, 2021 by Jilly

[Adsibob]

On 12/01/2021 at 18:44, PeterW said:

Ok so you can get round this. What sort of tiles have you got @Jilly..?

 

Prior to ridge venting the simplest way was to use tile vents - you’ll need to replace a tile every 3m or so in the top 3 rows of tiles. It’s easy done  - they push up the tile above to allow access to any fixing and then swap the tile for a vent. They are made to match the tiles. 
 

Alternative if you have a planning issue or non standard tile is to use lead vents - lovely looking but eye watering expensive if they are non standard sizes. 
 

These are the vents - about 3 times the price of plastic but lovely to look at ..!!

 

https://www.justlead.co.uk/product/roof-void-vent/

@PeterW thanks for this recommendation which may help me deal with a similar problem I have with a cold roof that I am struggling to ventilate due to a skylight being at the ridge where one would normally vent. Do you know if these lead vents would work on a roof that only had a 19 degree pitch?

[Jilly]

They've decided with the architectural technician to remove the ridge tiles and chop into the felt to create the ventilation as a solution. I'm not fully convinced and its a scary thing to remove the secondary waterproofing...

[coconutsaregood]

With hindsight, the carpenter should have created space between the plumb cuts of the rafters over the Universal Column (ridge beam), creating space just wide enough to form chimneys either side of the ridge tile batten, but still under the cover of the ridge tiles. The rafters  should not have met at the top in the traditional manner as there is no need with the dirty big steel ridge holding everything together nicely. 

Interesting topic on helping poor bats, good on you.