Under Slate felt , whats the story?

[Adam Aglionby]

Looking at getting late 1880`s 4 storey tenement re-slated, exposed position , scotch slates are slipping towards gutter at increasing rate, lead work evaporating etc. Flat platform in middle recovered 4 years ago.

Seem to have decided on Spanish slate as against reclaimed Scotch on balance of cost and apperance, some areas would have to be Scotch, not here.

Seems to be varying opinions on covering bleow new slates though, some say use a breathable fabric and no additional slate vents, others appear to be advsing non breathable and ` a few ` slate vents.

Seen loft to habitable conversions and BC seem very keen on lots of slate vents. Whole of this roof is above habitated space.

Whats anyones experience of undertile fabrics and the pros and cons?

Thanks Adam

[Jim K]

not part of trad. roof construction tho are they? why would they be needed in this instance?

underfelts should also allow water to drain off them over the eaves (usually lapped into troughings) and not allow water to pool or "pond" behind the fascia boards... and rot the underfelts and drain on/into the walls...

Jim K

[Dave Liquorice]

Had the modern breathable membrane stuff put in when we had our slate roofs redone a few years back on the basis that the normal sarking rots eventually and doesn't withstand exposure at all well. ie you loose a slate and the sarking fails where day light (and water) can get in between the slates... Along the gutter line our roofers put

18" (maybe 2') wide DPM with the membrane stopping 6" or so short of the slate edge on top of it. DPM doesn't degrade...

Inside the roof it is dry, there is occasional condensation but it does dry out no vents as such but it's still pretty drafty up there... The lofts is much brighter as well, membrane is a light colour rather than dark.

[Owain]

Does the roof not have sarking boards? Most traditional Scottish roofs do. I don't know if they need felt between the boards and the slates, but slate and boards should be naturally 'breathable'

Owain

[dom]

Had my roof reslated 2 years ago, with hand-finished Spanish slate - very happy with it all round.

Similarly had Tyvek throughout the whole roof, with additional waterproof felt/DPM on the lowest 18-24" and lapped into the gutters.

My roofspace is bone dry, all year round, no condensation. No roof vents, though there is an original (1873) arrow-slit type vent in the brickwork on one gable end.

My additional tip would be don't skimp on the detailing - leadwork, chimney & other flashings, chimney maintainence, gutters, fascias & soffits etc - get the lot done at the same time.

Get it all specified in the contract, and accept there may be cost overruns if it becomes apparent additional remedial work is required. Swallow the cost and get it all done.

[Rick Hughes]

Welsh Slate is the best in the world ... and no carbon offset bringing across Europe.

[Kipper at sea]

Wrong.. The reason Welsh slates are more expensive is the amout of waste in selection of quality and yes apart from Westmoreland slate Welsh are second to none.

[Adam Aglionby]

Tyvek seems to be one product mentioned, but its non breathable?

As long as it stays draughty guess is good, rot needs still air in general.at least dreaded dry rot does to get started,.

This is a terrace , so am concerned that ventilation is maintained.Yes, thre is sarking, hopefully in reasonable nick... Something local BC seems very keen on as well, as say seen habitable loft conversions where BC wanted dozen or more vents installed in each slope in a large semi.

Oh thats the other half, re-render chimney stalks, properely, some of the neighbours do show that cement work is a skill and one quite possible to get very wrong.

Mortar ` water gates` slump mortar at join of chimney and slates and hope water stays out, they have to go and get replaced with proper lead/zinc ones.

Its getting 8 individuals to swallow the cost and realise another patch up is a waste of money, its about 10 grand + Vodka And Tonic just for scaffolding , really don`t want a biennial roof patch up scheme.

Cheers Adam

[dom]

[Adam Aglionby]

Looking at cost, Welsh seems to come inat around double cost of Spanish, one company tried to sell us on Canadian!? which sems a bit of a carbon cost.

Is there a Euro/BS/BBA someat spec should ask for the slates to meet?

Thanks Adam

[dom]

I believe there's a BSxxxx, but practically the roofing company you select will be used to using certain suppliers. Get a recommendation, look at their work, and talk to some recent customers.

[Dave Liquorice]

Just bought a handful of (spanish) slates and the crates in the builders merchant had labels that detailed grades for weathering, carbonate content, and a couple of other things. So there is a spec or at least things they measure out there, google?

[Adam Aglionby]

27 roofers, lot dont` phone back or don`t turn up to quote, 11 quotes for wildly varying levels of works at wildly varying prices in very differnt levels of detail.

Now have preferred bidder just wabnt to make sure we agree on a spec as its been open to some debate, not having to buy a football pitch of reclaimed Scotch slate was bit of a relief though.

Spanish slate from quick google comes in everything from solidity of out of date sherbert to still around at next ice age, like to just make sure no questions about substitutions from spec to site.

Cheers Adam