Advice on venting loft

[AndrewB]

Hey guys,

We moved into our 1888 house about a year ago. Some of you will have seen a few posts as we have fixed up a few bits.

We always knew that the roof needed addressed and we are now planning on doing that.

We have a few leaks, few cracked slates, nail sickness, etc.

Plan is to remove all the old slates from front and back, use the best slates to refit onto the front with new lath and put cement tiles on the back (which will match existing extension anyway).



The plan is to felt the loft (no felt currently). Roofer reccomend 'pv400' but I think he means 'vp400'.

My question is about venting. I am no expert, but generally know that I might need a 'vented ridge'. Also possibly vents along the bottom edge?

If so, are there systems for this that look 'period'? Appreciate I don't have particularly fancy ridge tiles at the moment, but would even consider adding something 'even more period looking' (crested ridge?).

Would love your advice here. Can anyone set me on the right path?

 

[a twig]

Dry ridge systems

Howdy.. long time no see! Also not much progress since I last posted here a thousand years ago. I'm finally looking at replacing our late Victorian slate roof, which has decorative cloverleaf pattern ridge tiles, as per the image below. Also hip tiles which are overlapping ("crested", might be...

www.periodproperty.co.uk

Have a read of this one, when we did our roof the tiles and then breathable membrane provided plenty of ventilation, no dry ridge or additional vents required.

 

[AndrewB]

Thanks for the reply. Just had a proper look into what a 'dry ridge' is. The main advantage seems to be no mortar (so less maintenance).

Are all dry ridge systems vented? That was the main reason I thought I might need one.

@a twig was your roof slate like mine? Do you think if we replace the back half with new cement tiles and use best historic slate for the front... All with felt... we'd have enough ventilation? Was yours a similar project?

Roofer also mentioned putting '4 or 5' eves vents along the bottom front and a few less on the back (as the extension roof cuts in).

 

[a twig]

As per that thread, dry ridges do provide ventilation, it’s one of the main reasons they are recommended in the guidance.

Our roof I mentioned before was interlocking clay tiles rather than slates but our current place is slate and just has breathable membrane, slate and pre-dated the introduction of dry ridges and we get plenty of air movement up there.

If your roofer thinks you’ll be fine with just some eaves ventilation then I’d be inclined to agree. If it turns out that you are getting some issues it’s pretty trivial to add additional vents later on

 

[AndrewB]

It was actually me that mentioned a vented ridge first and he agreed. This guy comes reccomend as a 'slater' with some experience of these things, so il ask him to assess it properly rather than listening to me!

Was just reading about the breather membranes. Seems like witchcraft. Water tight from the outside in, air tight from the inside out... But completely vapor permeable?

If that's really true, then I expect we may not need the ridge vents as we don't currently seem to have any condensation issues. I think we have a lot of eves ventilation though. When I took out all the loft insulation I could see a thin line of light most of the way along the inside of the bottom edge of the roof. I think anywhere there wasn't light, was stuffed with 1938 newspapers!

I'm thinking vents at the lower edge plus the breathable membrane may be ok.

 

[malcolm]

When I had the roof taken off and put back on again the thinking for modern houses was the permeable membrane by itself was fine without any venting because their ceilings are so airtight. Now they realise they need a bit of ventilation and are recommending a dry ridge.

For old houses the permeable membrane is brilliant but you also need the eaves ventilation that should already be in place. There is no need for an additional dry ridge, and a dry ridge would look out of place on an old house.

 

[fernicarry]

Seems like witchcraft. Water tight from the outside in, air tight from the inside out... But completely vapor permeable?

Its air and water tight in both directions. Which way up you lay it doesn't actually matter other than the printed side is generally more UV resistant in case its left exposed for some time during installation so its best pointed outwards.

Water vapour will pass in the direction of higher relative humidity to lower. Outside generally is lower than inside due to being cooler but if the temperature difference is reversed water vapour can move from outside to inside.

sds-water-vapour-whats-it-all-about

 

[AndrewB]

Thanks @malcolm, thanks @fernicarry.

Roofer seems pretty keen to do the vented ridge. Not 100% if this is from his understanding of the property, ease of install or some other reason.

Would there be any negatives to doing it, apart from the aesthetics?

Wife and I are not that particular about maintaining this period feature but would like to if we can (we already have PV panels up there...). If we did want want to take the roofers advice and do the vented ridge, are there any 'period looking' products out there?

Ours is currently like this;


Presumably if we did want to reuse these tiles we could, but at least one is cracked, so might need to source replacements.

 

[AndrewB]

Didn't want to leave you guys hanging on this!

In the end we got these. Brand new roll top ridge tiles and a compatible dry ridge kit.

Trying our best to keep everything period. Not reclaimed or original but we think a fine compromise.

Super happy with them!

Install hopefully end of this week and beginning of next.

Up to the loft for me tomorrow.... Try to get some sheeting down on my brand new rockwool before all the lime torching falls on it....

 

[a twig]

Ooooh interesting! How will the tiles attach?

Don’t suppose you could provide links to where your sourced them could you?

 

[AndrewB]

Not 100% sure on the attachment tbh. I'm told the dry ridge kits I have are compatible, but it dosent make sense to me as a newbie.

Roof project going to take a week or something, so will check the attachment with the roofer and change if necessary.

Will let you know!

They are these ones;

Ornamental Ridge - Breedon Roof Tiles

Breedon Roof Tiles

www.breedonrooftiles.co.uk

Made locally near Belfast somewhere.

 

[AndrewB]

If you see here.... It does not seem very compatible to me... We will see tomorrow! Shouldn't be an issue getting the right kit if needed.

Maybe one goes each side... I don't know.



The official kit seems to have plastic thingies... May well end up needing it.

Breedon Dry Ridge Kit - Breedon Roof Tiles

Breedon Roof Tiles

www.breedonrooftiles.co.uk

 

[AndrewB]

Ooooh interesting! How will the tiles attach?

Don’t suppose you could provide links to where your sourced them could you?

Spoke to roofer today. Apparently we just use bigger screws and go straight down from the top of the roll into the ridge.

 

[alexander]

the advantage of the dry ridge is cross air circulation, vented at both high and low the eaves and the ridge,
even with breathable felt it is advisable to still vent the attic roof area,
as your membrane is your main secondary protection to at a latter date put holes in this to add vented tiles is just adding future leaks to your new roof,
your slates would have been allowing air flow into the attic void preventing a build up of condensation the torching would catch any drips getting under your tiles protecting your wood work,,
all roofs leak to a certain extent hence the reason for the membrane this will catch any drips getting under your tiles & direct it to where it should go the gutter providing felt support trays have been installed correctly as the membrane should not be lying directly into the gutter.
good luck Alex

 

[AndrewB]

All sorted!

Best of the slates refitted to the front and new ones on the back. VP400 felt and new lath. Copper nails... New roll top dry ridge and 10mm eaves vent the whole way along the bottom edge.

Very happy with the finish. Looks more or less like before with new materials. Ridge should weather in over a few years and look even better.

Thanks for the advice on this one guys.

 

[alexander]

did you put in felt support trays at the eaves

 

[Lacan07]

the advantage of the dry ridge is cross air circulation, vented at both high and low the eaves and the ridge,
even with breathable felt it is advisable to still vent the attic roof area,
as your membrane is your main secondary protection to at a latter date put holes in this to add vented tiles is just adding future leaks to your new roof,
your slates would have been allowing air flow into the attic void preventing a build up of condensation the torching would catch any drips getting under your tiles protecting your wood work,,
all roofs leak to a certain extent hence the reason for the membrane this will catch any drips getting under your tiles & direct it to where it should go the gutter providing felt support trays have been installed correctly as the membrane should not be lying directly into the gutter.
good luck Alex

Alex, how far into the gutter should the felt be? I've noticed mine hang quite a way into the guttering and are wet and green. I wondered if the moisture would wick up the material?

 

[AndrewB]

I'm not sure they did do support trays, first time it came up was when you mentioned it.

I do have the same as @Lacan07 with my extension roof though. Sits into the gutter and is green on/behind the felt.

 

[alexander]

if you don't install felt support trays & only have the membrane exposed at the end of the roof tiles it will create dampness, even the best membranes on the market are only uv resistant for a few months if the membrane is exposed to the elements it will just soak up rain water & deposit it in the brickwork creating dampness

 

[alexander]

its generally done as standard, building control will not sign off the roof work if it does not comply,