Advice on finishing new shallow pitch roof

[oldbutnotdead]

£8? Robbing gets! Found the bargain price I'd half remembered- it was one of the online places, £1.10 gross for 1500mm (if you bought 20)

Eaves trays usually (well all the ones I've bought) are profiled to sit on top of a single 20mm wide facia board. You don't need to fix the membrane to the trays- it should sit on top of them with enough length to reach the gutter. If it's flapping in the breeze then stick it down with gaffer tape or something while you're working. Oh yes, remember to overlap the trays by 100 mm or so

You don't really need to fix the trays either (gravity is your friend) but a nail into the rafter at the top edge (NOT through the membrane, just through the tray) doesn't hurt, especially since the trays are going to sit oddly on your double batten

Did some sums and yes if you've got a double batten at the front edge and 210mm deep tray then the tray is only running at 2 degrees, possibly less if yours are profiled for the single batten so are sitting oddly.

Cures;either tilting fillets under the trays (assuming there's some clearance between the top edge of the tray and the next batten) or sack off your final double batten and just use the facia board to support the last course of tiles (which is the conventional method and will make your eaves tray sit properly)

Do hope you've typed cavity tray instead of eaves tray cos otherwise I'm very confused. I'm playing with solid walls so cavity trays are alien beasts- they might be required in your existing walls (in the flashing line where your new extension joins the exisitng walls) to prevent driven water seeping through the existing wall and down into your new room. I'm no expert on this so couldn't comment on whether you'll need them- hopefully one of the more experienced types on here will pop up. You're going to be very tight on the flashing under those windowsills anyway- you'll be eating 63mm at the highest point of the tile which is going to leave no clearance under the sills for the 100mm flashing upstand.

Talking of upstand, is there any upstand on the felt at the house end? Can't see any in the photo (though it could be tucked in out of the way)

Gable end overhang-no idea, check the manufacturers spec. Oh yes, Fixmaster, Boo.

 

[mattu27]

Hello again, yeah I said that on the phone. 3.50 seemed quite reasonable yesterday as I was doing the job straight away but I did look at the same ones on ebay for the lower price.

Yes these seem like the the ones youre talking about, the only thing I was concerned about was the angle that they then pointed at when they were nailed down. I've made the mistake of not over lapping them aswell as I couldn't find a decent enough image yesterday showing figment. Will this be critical?. This was why I asked whether they should be nailed at the back as this would correct the reverse pitch when you get past the 200mm supported bit. (If that makes sense?)

I shan't bother bailing the membrane down to the trays in that case, I'll just drape it over them let the weight of the tiles support it from the base of the roof. The double batten is causing a bit of an issue but I couldn't see another way to do it and keep the end tile looking right, otherwise we would have had a small gap where the base tile meets the second row.

So could I use one of the smaller battens and sit it underneath the eaves tray at the top flappy bit to increase the angle? I'm just thinking of the membrane up from this which will then effectively have a mini trough feature? Or am I understanding it wrong? I suppose I could remove the top batten but the height of the fascia would still cause the near flat tray if I'm thinking right.

We had to move the windows three bricks up from where they originally were in order to get the minimum pitch that we needed without it looking daft. I'm hoping that we've got enough roof now for the flashing to be fitted effectively and do its job. As you might have guessed this house extension task is a relatively new one for me and I wouldn't have even said that I'm a novice. If we need 100mm from the top of the tile to the end of the flashing then we've got no chance!

And no, there is no upstand on the membrane at all, I'll have to add that on and maybe use some cut down dpc as we ran out of membrane by the end of the job. Would that suffice?

I've requested help from fixmaster, three days response time and I hope I've understood all the details that were required.

Could someone confirm the oversail and undercloak, finish the tile at 40mm past the cement board? Sorry, builder terminology

Thanks all, glad I signed up here.

Matt

 

[mattu27]

Sorry, understand now, fit under cloak/cement board 40mm past fascia then align tiles flush with this?.

Thanks, Matt

 

[ree]

Why not take some close up photos of the eaves area, the junction of roof and wall line, and the verge?

Are you intending fascia venting?

Has the fascia now been fixed all around the extension?
If not and its wood: then pre-fixing fascia (or any external woodwork) - prime, u/coat and two coats of gloss - all four surfaces. Then touch up after installation. Paint all mitre cuts.

With cavity trays in place then be v. careful when discing out for the flashings. The Cav tray lips sit on top of the flashing.

Last chance to check out the guttering and main roof tile condition before tiling the extension.

 

[oldbutnotdead]

Easy one first- felt upstand. Ideally you want 100mm up the wall and (if you're using odds and ends) enough down the roof to get under the top batten (that'll hold it still). DPM isn't ideal, you'd be better off with an offcut of felt if you had any left over but I'm sure people have done worse. Oh yes, you used all the underlay. Boo.

Felt trays- yes there is a trap there, if you lift the top edge with a bit of batten you'll form a trough in the felt which is not good. From looking at your sketches I don't see the problem with junking your first double batten and using the facia batten (positioned as it is in your sketch) to support the first course and that'll make the felt tray sit slightly lower which will improve your fall.

If you do need to lift the top edge of the felt tray you'll need wedges to support the tray, tapering so they stop below the 2nd batten. Still not ideal- the felt will still sag a bit at the edge of the tray- but puts you in with a chance. I think the proper way to do it would be using some 3 x 1 or similar and splitting it to form continuous wedge pieces- job for a sawmill, not a circular saw on a Workmate!. That way the felt would sweep up nicely.

Be careful that you don't get the top edge of the tray too near the 2nd batten- if you do then you can trap water under that batten.

(I'm not an expert in this, I'm laying my first slate roof at the moment. I was so confused by everything I'd read that I built an eaves section out of scrap timber, set up in the front room nice and dry and experimented with felting, setting out the battens, facia batten, trays etc. Very useful it was as well and I'd recommend it to anyone else who isn't sure how it will work in reality. I've still got the bits- looking at fitting a sun tube or skylight now and I think I'll be mocking that up on the ground as well!)

Near flat tray (2 degrees) will be OK. Not ideal but OK. More will be a bonus.

Overlap on the trays is a good thing. Sounds as if you've spiked them to the double batten already- a really nasty compromise will be Flashband the joins. The joins don't have to be watertight but a gap between them will give a weak point in the felt (over time it'll sag into the gap, chafe and fail). Flashband sticks to those trays really really well.....

Flashing/cavity trays in the existing wall. Tricky one- again I'm NOT AN EXPERT but you won't be able to flash conventionally under those window sills. BUT the sills will give a lot of protection from water at that point so as long as you bed whatever flashing you're using (please say you're using lead) well into the mortar under the sills you'll probably be OK.

You may be best treating those sill areas as separate flashes (so cut into the mortar at undersill level across the windows and continue 200mm or so either side of the sill), flash those sections with their puny 20mm upstand and then cover the ends of it with your main flashing run (which will be 1 course above undersill level). When you're raking out the mortar near the windows keep an eye out for cavity closers or DPM especially under the sills.