Best course of action for a roof with no ventilation

[K Wimberley]

We are busy renovating a property built in the 1930s. As we go along we inevitably find things that are a bit surprising, forcing us to change our initial plans.

We would like to ask for advice on what the best course of action is to clad the upstairs area under the roof.

The situation
The upstairs floor of the house is built under the roof (loft space). Pretty standard with an additional small roof space above and small slope and low structural partition on the sides. It has been that way for many years. It is currently not insulated (with minor exceptions) and clad in a kind of fibrous boarding, which we will need to replace anyway due to the internal changes we are making.
And now for the bad and important bit: There is no ventilation in the roof space, which probably accounts for the mustiness and slight dampness on the inner paper lining under the (non breathable) roof felt and the mould growth if the windows are left closed.

There is no easy solution to providing ventilation. Under the eaves the external walls (granite cavity walls) are built right up to the roof. Diamond drilling air vents the whole way around would risk splitting the granite and be very expensive. There are no compatible venting tiles available that would match the tiles on the roof and as the roof space is lived in so you would need one for every channel. The best course of action - taking the tiles and battens off, adding insulation, replacing the felt for a breathable membrane, adding ventilation and re-tiling - is way out of our budget for the time being.

So given that we are living in an non-ventilated cold roof space (!) what is the best course of action to clad the space without amplifying the potential risk of condensation/dampness. Ideally we would want to do this in a way that leaves the option of replacing the roof in the future, without having to redo the inside of the space.

Is it a good idea to put a VCL in to reduce the amount of damp air going into the roof space/channels between the wooden beams? I assume it can't make the situation worse! I also assume that putting in wool between the rafters is a bad idea at present as it would prevent the damp air going into the upper roof space, but maybe if we have the VCL this wouldn't add to the existing risk? Go from bad to bad but less wasteful. Or use materials that can hold on to the moisture and regulate the environment until windows are opened, etc.
Our original plan of keeping everything breathable and as sustainable as possible (wood fibre and sheep wool insulation, etc) doesn't seem to make sense when the outer layer isn't breathable and would no doubt add to condensation risks.

Before everybody cries you have to bite the bullet and redo the roof, this simply isn't an option at the moment (financially). So it's how to make a bad situation live-able and if possible a little better.

Any advice greatly appreciated!
Kaspar

 

[theprinceofdarkness]

Is it a hipped or a gable roof? What about the ridge tile?
Frank

 

[K Wimberley]

Hi Frank,
thanks for the speedy reply.
Gable. With two further small gables coming off it.
Ridge tiles could be replaced for a ventilated ridge, but without ventilation under the eaves I believed this wouldn't be that useful.

 

[freddiemercurystwin]

I expect you would be able to find a suitable under tile eaves vent.

 

[K Wimberley]

Hi Freddy, I did look (and call, ect), without success. It was the first thing we looked into once we realised there was no ventilation. It would also need a lot of them. Almost the whole way along for each channel (as the channels are clad inside). But still the cheapest option if we can find something. I assume by under tile you mean a tile that has a vent that goes through to the channel. Thanks for your message, Kaspar

 

[freddiemercurystwin]

I mean a continuous vent that runs under the bottom tiles supported on the top of the fascia, or whatever the tiles are resting on.

What do you mean by channels?

 

[K Wimberley]

Now I get you. Not so easy here. I need to do a drawing for you really. The roof overhangs the exterior walls (windy location, etc). Here you have the fascia. Then you see exposed rafters on which the tiles/battens/felt rest. Then the granite external walls go right up between the rafters. Why I don't know. So ventilation tiles can only be used beyond this point (about a foot up the roof).

By channels I mean space between the rafters (channels as the slopes are clad inside to make the living space upstairs).

 

[freddiemercurystwin]

I'm not talking about ventilation tiles.

Anyway do a doodle and add photo of the tiles/eaves.

 

[K Wimberley]

Sure, I understand the strip and have seen diagrams, but there isn't a place for it. Pic soon, k
K

 

[K Wimberley]

Here you go. No soffit.

https://app.box.com/s/6hre3isr8m4cgjfbeodp24wwgchre4s5
https://app.box.com/s/fl9ol5xluntm8ci2x65indiah7gckdly
Does this count out the strips?

 

[K Wimberley]

If I were to use vented tiles (presuming I found some that would fit and the money to do it), this would involve LOTS of them as the rafters are quite close together.

 

[freddiemercurystwin]

You don't fit under tiles vents in the soffit or in the tiles, they sit immediately under the tiles. Thought you were gonna do a doodle? We need to understand the the configuration of the wall, rafters, membrane, battens, tiles, fascia & gutter. And that board on top of the rafters?

 

[K Wimberley]

Thought the images kind of explained the situation clearly enough. I can do a sketch later in the day.
Configuration in short: The tiles rest on the battens, which rest on non breathable felt, which rest on the rafters (with a paper lining between that is torn up in most places due to low level damp). All done in the 1980s I believe. The ply you see in the pictures is just around the edge, not continuous over the roof. Exterior walls going up under the rafters are masonry granite walls. The blockwork after the cavity does not go up into the rafters.

 

[K Wimberley]

So would you replace final batten with strip vent and have felt go over this to allow ventilation between the rafters. Still an issue with the ply perimeter. We will probably get somebody to do this for us, but I would like to know what the options are and what to research first. Thanks for your help by the way. K

 

[freddiemercurystwin]

No battens are removed, generally speaking the vent goes between the bottom of the bottom row of tiles and the fascia or maybe the top of the wall but it depends on the relationship of all of the various components to know what is possible or not especially that plywood board. Presumably there is a gap (albeit maybe small) between the top of the wall and the underside of the felt?