Slate DPC and New French Doors

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Hi Everyone,

I'm just about to place an order for some double-glazed UPVC french doors which will replace an existing window.

I'm reasonably confident doing the work and have replaced several windows before but had a question about measuring accurately for the new doors.

The issue is that there's a slate DPC on top of the brick course that the bottom of the door will rest on. My question is - do I measure to the top of the slate DPC and aim to install the doors on top of the slate or should i measure to the top of the bricks just below the DPC and when I install it, remove the slate and lay it straight onto the bricks? (marked A and B on the photo below) There's about a 20mm difference.

I know the UPVC will act as a DPC so it won't necessarily need the slate but didn't know what was best practice.

Thanks for any advice in advance (photos attached to make it clearer)
IMG_1998.jpg
IMG_1999.jpg
 
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From experience the cement bed always crumbles away to nothing anyway by the time you get the course of bricks off it, its pointless trying to save it. The course of bricks you want to lay the door on though looks a bit up and down so be careful in measuring the height, I would allow enough to lay the pvc cill on a bed of mortar.

Also before placing the door onto the cill remember to put a good bead of silicone along the it just back from the back edge and also the sides in an L, stops water tracking backwards between the doorframe and cill, sealing the sides stops the plastered corners getting damp inside too.

Is there a lintel in place too?
 
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Thanks for the reply and advice - that's really helpful.

I'd normally take off 10mm anyway from the actual height so what would you recommend increasing that by to allow for the bed of mortar? (I don't think the top of the brick course is more than 5-10mm out along the length)

Yes, there's a lintel and I'm petty sure it's a catnic lintel as I've drilled through it previously when fitting blinds. To be honest, as the doors will be exactly the same width as the windows I haven't worried too much as I thought whatever lintel was in place for the window would still be ok for the doors - have I missed something there? (quite possible!)

Thanks again for your time and advice.
 
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Not missed but when you say the doors will be the same width i get that but the window has 2 mullions with which to support the brickwork if it were actually resting on the window where as if you fit french doors you have nothing so the weight could bow the head frame down and foul the door sashes however you say theres a catnic in there so all's good, just don't lift the frame right up otherwise it will follow the bow. I'd probably knock another 10mm off for a mortar bed, bed the cill nice and flat and level, nothing worse that a brick corner poking up that bows the cill up and the doors forever catching along the bottom even with some proper heavy duty toe and heeling

Are the doors opening out or in?
 
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That’s a really good point about the lack of mullions in the French doors - I’d never considered that but I’m sure there’s a catnic but might double check tomorrow before ordering. So I’ll subtract 20mm from the actual height and hopefully that should be all good and allow for a 10mm mortar bed and the usual gap.
They’ll open outwards and I was going to go for double glazed instead of triple cos I was worried about extra weight of triple over time and strain on hinges etc. Hope that’s right choice but wasn’t 100% either way.
 
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Good choice on double not triple, doesn't get cold enough for there to be a quantifiable difference plus the extra weight on the hinges, but as for glass spec i don't know what your supplier has quoted or uses but at least put an A rated unit x2 in, something like planitherm total+ inner pane with a warm edge spacer with argon
 
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Great - thanks. The spec is:
  • Inner pane – Pilkington KS (A+)
  • Outer pane – Pilkington Optiwhite (A+)
  • Gas filling – Argon Gas
  • Spacer bar – SuperSpacer
  • Thickness – 28mm
  • U-value – 1.2
Doesn't mean much to me but sounds like it matches what you've recommended. Thanks again for all the advice - will place an order today.
 
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Obviously your supplier has a deal going with Pilkington so fair enough, KS is pilkingtons version of Saint gobain Planitherm, the optiwhite which i didn't quote gives you better light transmission as its low iron and has no green in, super spacer fine as well as argon although the argon will have all but leaked out in 3 years anyway, overall good spec of unit
 
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Out of interest, if you were going to do the job I'm planning to do (without the cost of the actual door), what would be a rough figure you'd expect to get quoted for it?
 
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You'd need to get one the fitting guys to price that up, Gazman, DHFrames or God, I'm just a service engineer and don't get involved in pricing brick outs, if i were to guess then i'd say 1st day remove window, brick out both skins and fit and glaze doors, 2nd day fit internal hardwood threshold and skim out, 3rd day cleaning and sealing, 3 days x £200 a day plus a tiny amount for materials
 

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