Natural Stone Front and Window Reveals

IPFreely

Hi,

My ground floor block work is just started and last night I met a local stone mason to speak with him about finishing the front in natural stone (Liscannor - Cut Drystone).

One of the things that came up though which he said would be important for the blocklayer is how he (the mason) would be finishing the window and front-door reveals. He told me there are 3 ways he can finish the reveals.

These are shown (sketched roughly) in the attachement:

1) The window is fitted as per normal, the reveal is plastered in to the window as per normal and the stone stops as the edge of the outer leaf

2) The window is fitted a little further back, the outer leaf is stopped approx 4 inches short of the inner leaf edge and the stone is turned round the corner finishing up against the edge of the window. DPC runs as shown in navy in the diagram

3) The window is fitted the the outside of the outer leaf and the stone is brought to the edge of the outer leaf (not keen on this)

The choice he said is my own but method 2 would be more expensive due to the extra work involved.

I do prefer method 2 as I like the way the stone returns to the window. However, my concerns are around the area of water penetration and also heat loss using this method. I don't see how the window can be adequately sealed against water coming in and also heat escaping.

Method 1 to me seems to be the safest as you can plaster right up to the window and ensure you are positioned correctly over the insulation and sealed.

Does anyone have any opinions on the method 2 above? How have other people that have built a natural stone front handled this detail? Any suggestions appreciated as I am a loss.

Thanks!

ThePiedPiper

We finished our house as per Option 3.. We've a 4 inch half red-brick return.
The main reasons we chose this is if you have a window reveal that's 8 or 9 inches (full red brick), the window's very far back and it's going to leave it a little dark inside the house.
Other reasons came up, such as if we'd used the full brick, the window sills would've been 15 inches wide. Instead we used 10 inch sills (a fair bit cheaper). Of course on the negative, we'll have to get bigger window boards for inside but I quite like the idea of wide window boards anyway, so that's fine.
We looked at houses with window set back 8 inches and others with windows back 4 inches from inside and out and we decided the light issue inside was what decided it for us..
Each to their own though..

ronboy

I done option 2 and i'm very happy with it and the damp course would be better on the outside of the window between it and the stone reveal rather than inside...thus keeping water out

mickdw

DO NOT do No 3. The outer blockwork course is a wet course and the window cannot be placed outside it like that without an almost certainty of damp getting through to the internal house.
The window has to go in its proper position just inside the vertical damp regardless of wall thinkness outside. No 2 is a good detail appearance wise but i wouldnt agree with the blue line if that is a dpc shown. It shouldnt be going around the window to the inside of the house. A simple vertical dpc at the outsie of the window frame will work perfectly provided its wide enough to cut off any connection from outside to inside.
In exposed areas a plastered reveal is best for sealing.

IPFreely

Thanks for the replies...I will be going with option 2. After spending the weekend driving around most house are finished this method and any masons I spoke to assured me this would not cause any issues

sydthebeat

option 3 is doable, but not as per that detail. The rear of the window frame should not come further than the inner face of teh outer leaf. I personally suggest this detail as it allows a deeper window board and gives the opening better proportion. Options 1 + 2 are out on that basis.

Its easy to do. I recommed filling the cavity at the opening with rigid insulation. The vertical dpc is left wide enough to be folded on two planes, the inner + side face of the outer leaf, generally 200mm DPC is required. This is full protection from wind driven moisture. The 100mm of outer leaf then exposed on the external is rendered. Most importantly, the stone veneer should be carried about 30mm past the opening face so that the plasterer has something to render against and to give the finish a completed look.

mickdw wrote: »

DO NOT do No 3. The outer blockwork course is a wet course and the window cannot be placed outside it like that without an almost certainty of damp getting through to the internal house.
The window has to go in its proper position just inside the vertical damp regardless of wall thinkness outside. No 2 is a good detail appearance wise but i wouldnt agree with the blue line if that is a dpc shown. It shouldnt be going around the window to the inside of the house. A simple vertical dpc at the outsie of the window frame will work perfectly provided its wide enough to cut off any connection from outside to inside.
In exposed areas a plastered reveal is best for sealing.

ThePiedPiper

sydthebeat wrote: »

option 3 is doable, but not as per that detail. The rear of the window frame should not come further than the inner face of teh outer leaf. I personally suggest this detail as it allows a deeper window board and gives the opening better proportion. Options 1 + 2 are out on that basis.

quote]

Thanks syd,
you've put my mind at rest now... In every respect, my mason is an absolute perfectionist so I'd have been very surprised if he'd done something that was going to cause problems... delighted to hear that it shouldn't be an issue..

donal1981

Does anyone have an accurate drawing\detail of option 3.
I will be going for this option, so i am really concerned about the DPC detail for option 3.

Is this option the most commonly used?

Also,is it ok to stick DPC together, if i run into a situation where i need an extra wide bit of DPC?

donal1981

[QUOTE=sydthebeat;62098711 The 100mm of outer leaf then exposed on the external is rendered. Most importantly, the stone veneer should be carried about 30mm past the opening face so that the plasterer has something to render against and to give the finish a completed look.[/QUOTE]

sydthebeat - Can you elaborate about what your talking about in the above instructions? Thank you in advance.

hbarstone

option 2 most common, looks very well and widewindow board gives oldfashion effect like old stone houses. no matter which choice 1,2 or 3 will get same amount of light. thickness of wall in total be same so when say sun at angle will get same light. if windows narrow and want more light suggest option 2 and taper back enternal wall at angle like see in old stone houses as allows in lots more light. water and heat loss not problem once care taken with dpc etc. wishing you sucessful project

atech

Probably too late for donal and runforestrun but anyway:

From a cold bridging perspective, option 3 would not the best option especially if you are going to the expense of buying thermally broken window frames.
The window is best kept in line with the insulation zone.

Personally I'd perfer the appearance of option 2 over option 1, (with just vertical DPC as mickdw said), there is more labour involved in it though.

FergusD

You should be able to have a variant of option 3 similar to Syd's without the cold-bridging problem I think (hope!). We were planning to go for option 2 as per the homebond book and so have an outer leaf of blockwork 100mm short of the inner leaf (150mm cavity), but have decided from an appearance point of view to go for a variant on option 3 - mainly due to having windows in plain plaster close to windows in stone, then having the windows different distances back from the face of the walls, etc. We also like the deep window board from the inside.

This will involve Syd's DPC, but rather than the outer leaf of block coming close to the interior of the house at that corner, as we have the space left for option 2, we fill in that 250mm with insulation. The windows then get strapped back to the inner leaf and we close off the cavity (now just insulation) with plywood or plasterboard, before taping for airtightness.

Here's a very rough sketch of what I'm planning. As you can see we don't have the detail totally ironed out yet, but it should be doable I think. This is based on some of the stuff linked from this thread:

http://www.boards.ie/vbulletin/showthread.php?t=2055861004

Anyone better qualified care to give any drawbacks of or improvements to "the plan"?

Thanks,

Fergus.

atech

Fergus,

The thread you linked too is slightly old, soldsold came back with his proposal in another thread and I gave him my opinion on it.
I also showed a detail of how I would install a window in a 150mm fulfill cavity (i'm open to alternative suggestions).

http://boards.ie/vbulletin/showthread.php?t=2055883818

A varient of Option 3 may be possible but the previous two sketches didn't show any thermal break which is why I said it wouldn't be the best from a cold bridging perspective.
Your detail probably shows too much of a thermal break. It would be quite difficult to have the stone come that far past the blockwork especially at the head detail.
But even with 25-30mm of insulation around the frame at the head and jambs, I would still have concerns about cold bridging at the cill, the DPC arrangement over the window and increasing the lenght of straps to meet the inner leaf. (especially in cavities 200mm+).

gerrymoff

Hi being a stonemason myself this(see attachment) is the way i construct the ope and its what i recomend as it reduces cold bridge, no dampness can pass and the stone is layed tight to the wndow frame so there is no unsightly plaster to spoil the stone. The block is simply returned across the cavity but left approx 30/40 mm less than the external block to allow for insulation and DPC and there is also a break left in the external block for the insulation and DPC to pass through and meet with the cavity insulation. Also make sure the block layer at the top of the window runs the DPC from the inner leaf out across the cavity through to the external leaf and down over the outside of the window.:)

atech

gerrymoff wrote: »

Also make sure the block layer at the top of the window runs the DPC from the inner leaf out across the cavity through to the external leaf and down over the outside of the window.:)

Hi gerry,
That jamb detail makes it much easier to strap the windows to the sides alright but i'd still be a bit iffy of what happens at the cill and head.

See attached detail. If using conventional concrete cills there is still a cold bridge here and at the sides (where the cill and return block meet), and where are the windows strapped to at the head if the DPC comes over the frame as shown?
I'd also wonder about what is supporting the inside window board near the frame?

gerrymoff

It is very hard to stop cold bridge totaly but you can reduce it greatly. In regards to fixing the window at head level the DPC should exit the external course above the concrete lintel then down over the top of window leaving the bottom of the lintel free for fixing the window.

In regards the cill we usualy stop the internal block at the bottom of cill level then close the cavity then put approx 30 to 60mm insulation tight to the window and fill up to the bottom of window board with concrete or mortar leaving a solid base to fix window board.

Hope it helps:)

atech

I agree it's very difficult to stop cold bridging with cavity wall construction and the way you have described it is probably the best traditional method of closing the jamb.

I guess what I was trying to show is that it is possible to entirely eliminate cold bridging with 1 & 2 (although traditionally it has not been detailed correctly so doesn't happen too often) but I can't see how with option 3.

I had actually shown my DPC over the lintel in the sketch in other thread I linked a few posts back and soldsold made a good point about all the mortar falling from the blockwork collecting there.
So incase anyone reading will be doing it this way make sure your blocklayers use a board or something to stop mortar falling into the cavity.

soldsold

gerrymoff wrote: »

In regards to fixing the window at head level the DPC should exit the external course above the concrete lintel then down over the top of window leaving the bottom of the lintel free for fixing the window.

I had understood that a lintel is designed to need a block course above it to bond to, and only then is it at full strength? A couple of the architects on this forum have made this clear a few months back, and the point being that if the lintel has a dpc on top of it instead of a mortar bed and blockwork it can sag and make windows stick when opening or glass crack etc

Im considering supporting the sill internally with angle steel to stop the sill from twisting backwards towards the cavity when the weight of the triple glazing goes onto it, this should help to allow me to avoid using straps over the windows

mossfort

soldsold wrote: »

I had understood that a lintel is designed to need a block course above it to bond to, and only then is it at full strength? A couple of the architects on this forum have made this clear a few months back, and the point being that if the lintel has a dpc on top of it instead of a mortar bed and blockwork it can sag and make windows stick when opening or glass crack etc

Im considering supporting the sill internally with angle steel to stop the sill from twisting backwards towards the cavity when the weight of the triple glazing goes onto it, this should help to allow me to avoid using straps over the windows

we have always put the 12" dpc directly onto the lintel and never had any problems . the only place where a lintel will sag if its over acertain span and is not supported after being fitted. for wider openings the engineer will probaly specify rsj,s or heavier lintels.

jwshooter

im doing a house with option 3 , DPC has to be right ,no second chances .

make sure heads have extended DPC say .5m each side ,also make sure its tight to the wall .

you can use silicone to seal it .