Window sill options - opinions please?

Forums › Home Workshop DIY › Window sill options - opinions please?

Fred99

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#129584 20-Sep-2013 13:55

I was going to post this in the home workshop forum, but it's not a case of how to do it, unless someone did happen to have a eureka suggestion (foir which I would be very thankful)
In re-cladding a formerly brick house, there's an issue with the "look" of deep reveals left over from the 4 1/4" old brick plus cavity, where the window sills had sill tiles. It's not a (building) consent issue, either option is acceptable from that POV. But I need to decide to get drawings done - as consent is needed for the whole job.
My architect suggests that the sills should or could be extended past the new cladding rather than left as, with the effect that they would "step down" to a bevel in the sill reveal in the new cladding. I reckon that it looks ok leaving the sills "as is", as the new sills will look to deep. But my opinion might be tainted by not really wanting to do the extra work. My very crude comparison images below. Opinions please?

nickb800

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#899012 20-Sep-2013 14:11

From a weather tightness point of view, I'd extend the sills. Sure the render(?) over the brick sill is watertight now, but it will degrade over time if exposed like that - an extended wooden sill just adds an extra layer of protection.

Inphinity

2780 posts

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#899013 20-Sep-2013 14:11

I actually think it looks better with the narrower sill, but that personal preference.

Fred99

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#899023 20-Sep-2013 14:21

I won't be a weathertightness issue - there aren't any bricks, the existing sill extends over the cavity, with a PVC flashing which will be embedded in the new cladding plaster system. Because of the way it is at the moment, there's a layer of building paper on the framing holding in batts, over that there's 9mm ecoply, flashed in all the joins, fixed with SS screws, over that will go new timber framing attached to the studs (rather than using a batten system) to support the new cladding system (panels fit longitudinally - staggered). Next time (but hopefully not) the old house decides to shake like a wet labrador, I don't want it to fly to pieces.

Fred99

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#899037 20-Sep-2013 14:43

Ok - I suppose I was pushing it a bit by posting in the general off topic forum as I was after "non expert" opinion only, but now it's been shifted.
Inphinity - I agree - it looks better to me too. I emailed this to my wife - she is 100% undecided.
Seeing as this is now in the home workshop forum, the difficulties with extending the sills are that there's an uneven (+/- 10mm or so) depth between the framing and the top of the perimeter foundation. The entire perimeter will get re-plastered before the cladding is installed. If the sill overhangs, then it's going to need to overhang by enough to allow for a drip groove underneath, so about 15mm at the bottom. Leaving the sills as-is, a pre-made flashing simply slots into the existing drip groove - easy. If extending the sills, I don't know exactly where the vertical plane of the new cladding will sit now, but trying to fit extensions to the sills after the cladding is installed would be very tricky. I think I'd need to cut (or probably carefully plane - as there's no room to get a saw down the entire length of the sill) the front edge now - before cladding goes on - then measure and adjust the "extension" after the cladding is in place by running through a thicknesser, then fit with dowels and epoxy glue (and probably a few tech screws), fill, prime, and paint. It's one of those situations where it seems easy, but my guess is it could be a can or worms once under-way, also much of it will need to be done using scaffold - so I don't want to be mucking around for weeks.

minimoke

750 posts

Ultimate Geek

#899108 20-Sep-2013 16:32

I'll go with the "extended" sill option. I reckon the "short" sill looks like a reno gone bad. It will look like a rockote do up rather than an integrated, considered build. It’s not the easy option but I reckon you have to find a way of extending your sills but it looks like it will be problematic. You have to work around the sash window; any join is likely to split and trying to get the two planes to be the same is remote - something will be out of whack. What about doing a join and then making a "flashing" that sits over the whole sill so you have one flat surface. Folded steel or a plastic might do the trick. Other than taking the windows out and putting a new sill in I'm not sure there is an easy (and cheap) option.

Disrespective

1925 posts

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#899118 20-Sep-2013 16:40

I'm an architect and I prefer the wider sill option. It'll be simpler to build, simpler to maintain and visually more appropriate. In my mind anyway.

Dratsab

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#899168 20-Sep-2013 19:20

minimoke: I'll go with the "extended" sill option. I reckon the "short" sill looks like a reno gone bad. It will look like a rockote do up rather than an integrated, considered build. It’s not the easy option but I reckon you have to find a way of extending your sills but it looks like it will be problematic. You have to work around the sash window; any join is likely to split and trying to get the two planes to be the same is remote - something will be out of whack. What about doing a join and then making a "flashing" that sits over the whole sill so you have one flat surface. Folded steel or a plastic might do the trick. Other than taking the windows out and putting a new sill in I'm not sure there is an easy (and cheap) option.

Disrespective: I'm an architect and I prefer the wider sill option. It'll be simpler to build, simpler to maintain and visually more appropriate. In my mind anyway.

I agree with the sentiments of these posts, especially the "visually more appropriate" part. I'm a complete layman when it comes to stuff like this but to me, the extended sill looks tidier, suits the sliding windows a lot more and gives a great feeling of depth.

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Fred99

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#899245 20-Sep-2013 21:34

Thanks for the replies. So - the extended sills are more popular - especially with "expert opinion" which is just what my architect was saying. Just to clarify, while this would be simpler for a new build, for the job at hand, re-cladding to work with existing window joinery, it's much harder to extend the sills.
Tonight on the way to dinner, we stopped and took a look at a house of similar vintage and design which had suffered the same fate as ours in EQs, and had been clad in lightweight materials. They had the same issue with the sills. The end result looked pretty good we thought - much better than my photoshop job. Big difference was colour, so I tried this:
sidebyside2

I think I can live with that (dark sills are a bad idea anyway - WRT durability of paint). Intended end colours would be warmer than above. I think we can also easily run a moulding up the side of the frame in the same colour as the frame, so that the sill doesn't protrude out further than the edge of the frame - and it looks more "evenly inset" all around. The top of all windows extend to soffit height, with T&G eaves - so no problems there.
So does anybody who preferred the "look" of the extended sill agree that if painted off white (or a colour matching the frame - rather than in contrast to it), then the inset sill is much more acceptable?

Incidentally, this is the reason that we won't be replacing brick with brick (same area of the house):
brick

The conventional opinion is that brick failed because of in adequate tying back and mortar. This was not the case here.

mattwnz

20141 posts

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#899269 20-Sep-2013 22:22

Tying back may not have stopped that sort of damage as you will get cracking in the mortar from EQs. Bricks really aren't suitable for EQ areas in my opinion. The window sill is better extended, but the ends of the sill in the internal corner sill junction, are a bit of a risk, and you could get rot if not flashed and done properly, including isolating from the plaster with DPC. Normally windows are not recessed, the out edge sits on the outside of to allow drainage. You don't really want water drain through a cavity, that is there for secondary protection.

What is the substrate that is being plastered over, I am not sure if you mentioned it. Polystyrene?
Personally if I was having recessed windows like you have got, I would do it with solide concrete block, and plastered over a membrane coating like resene X200.

Fred99

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#899277 20-Sep-2013 23:08

I agree that brick veneer isn't suitable for most of NZ, BRANZ did their own tests, and even lightweight 70 series brick starts to fail at 0.23g/1hz/10 cycles. They still stand by it though, LOL.

I don't want filled block - or anything heavy on the perimeter foundation. While filled block might survive in some cases, the house in on a sloping site, and the foundation goes from ~0.5m to ~ 2.4m height. It survived pretty well, but there was clearly enough flexing going on to cause vertical and diagonal cracks through the face of the brick veneer.

So yes - poly, 75mm. Packed out using timber from the studs (rather than the more usual metal battens), and laid horizontally, staggered, then plastered. Have looked very carefully at aerated cement (Hebel/Celcrete) as well. They all cost about the same, Poly is a better option in this case IMO.

Yes - which ever way I deal to the sills, where it butts against the cladding needs to be thought through. OTOH, it was simply butt against the original brick for 50 years and no problems with rot at all, 4 ft eaves mean that the external walls seldom get wet - most never see any rain.
Part of the house was clad in weatherboard, some of which was stuffed by falling chimneys etc, so will be replaced with linea - no problems with window/door joinery in those areas.

gazbo

89 posts

Master Geek

#899568 21-Sep-2013 23:27

I would use a wider trim that extended over the cladding. Make it from a single piece by planing a 10mm deep sloped rebate in all but 20mm of one side leaving the 20mm thick side to lap over the cladding covering off the cladding top edge and acting as a drip edge at the same time.

pctek

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#901396 23-Sep-2013 18:45

Extend the sills....it looks manky, regardless of water issues or not.
Recladding? Hmmm, not a fan of it....

Fred99

13684 posts

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#901403 23-Sep-2013 18:53

I'm not going to extend the sills - that's decided. We'll paint the existing sills a light colour.
Recladding isn't an optional thing - there's no permanent cladding on the house.