Any Architects on here?

[Mulberry View]

I'm really pee'd off. I've spent weeks working against what seemed to be an unachievable timeline to get our building ready for the Zinc contractor scheduled to arrive on site at the beginning of July.

 

At this point, I've got 95% of it in hand and feel that I can push to meet the timings, save for one detail. The flat roof link/gutter between the 2 halves of the building.

 

 

My now estranged Architect has left me with an absolute headscratcher to sort out and this is now most probably the one reason I'll miss my the roof deadline and god knows what consequences with the contractor and the hefty deposit we've paid them.

 

I'd gladly try to lay it all our on here, but I think I need an Architect/Technician to help me sort this out. Is there anyone on here that can save my bacon? I have touched on aspects of it on here before, but I need decisive action as the 5% is consuming waaaaay too much of my head when I need to be sorting out the 95%. I'm gutted that this one detail could see weeks of hard work be in vain.

[Dave Jones]

awful design to squeeze in 2 windows. lead would be my preferred osb under it. could use rubber also.

 

would have looked soo much nicer if those roofs were joined.

[Kelvin]

Have you asked your zinc roofer what they think? They’ll have seen every manner of detail joining two different sections together. Other options are GRP or a membrane like Alwitra or Sarnafil but those would have to be done first I expect . It is a slightly odd difficult junction. 

Edited June 18 by Kelvin

[Mulberry View]

1 hour ago, Dave Jones said:

awful design to squeeze in 2 windows. lead would be my preferred osb under it. could use rubber also.

 

would have looked soo much nicer if those roofs were joined.

 

The rearmost window is not problematic, it's the front one. I only have 350mm from the top of the Posis in the flat roof section to the sill. My Architect drew a hopper which I like, but the flat roof really needs a parapet wall approach, which there isn't really enough room for.

 

 

We opted to beef the insulation in the main roof areas up to 200mm, but this makes the problem in the flat roof section worse unless I can get away with less insulation in that area.

 

We discussed constructing a parapet wall that follows the roofline down and gives the illusion of it continuing to meet the adjoining building, but that window is right in the way of that. Sill is already 900mm, didn't really want to push it up much more.

 

 

[Mulberry View]

1 hour ago, Kelvin said:

Have you asked your zinc roofer what they think? They’ll have seen every manner of detail joining two different sections together. Other options are GRP or a membrane like Alwitra or Sarnafil but those would have to be done first I expect . It is a slightly odd difficult junction. 

 

Yeah, had the Zinc guy turn up this morning to see how I'm getting on. He came up with some ideas, but nothing that I can get on and build without better understanding.

 

I had resigned to it being EPDM or similar, but i believe the Parapets need to be 150mm above the flat roof?

[Thorfun]

@ETC is an architect

[ETC]

Can you fall the flat roof towards the wall with the problem window dropping down into a gutter running along that wall formed by reducing the flat roof insulation thickness in the gutter.

Edited June 18 by ETC

[ETC]

I am not sure if this will work - the levels and falls would need to be fully worked out. You’d need to start from the bottom of the window cill and work out your levels from there. The gutter insulation could be reduced to the absolute minimum - I suspect 150mm could probably get your U-value but this would need to be checked.

[Mulberry View]

1 hour ago, ETC said:

I am not sure if this will work - the levels and falls would need to be fully worked out. You’d need to start from the bottom of the window cill and work out your levels from there. The gutter insulation could be reduced to the absolute minimum - I suspect 150mm could probably get your U-value but this would need to be checked.

 

That's an awesome help. You wouldn't believe this but the penny dropped for me earlier this evening with a similar solution. What you've done pretty much nails it, but I'll try and draw what I have in my mind and perhaps run that by you?

 

I'm so grateful for you taking the time with the above.

[ETC]

Happy to help.

[Mulberry View]

1 hour ago, ETC said:

Happy to help.

 

Here's a rough idea of what I propose. If this could work, it would be the preferable option.

 

Horizontal Parapet wall on the green lines....

 

 

Integral gulleys on the thick red lines. Outlet into the denoted hopper. Flat roof falling in the direction of the red arrows...

 

 

Very roughly this. The scale is off and the measurements are for guidance. We had planned to fit 200mm PIR into the main roof, so I guess we need to do the same in the flat roof area? 120mm meets our declared as-designed SAP, but we want to do much better than that. I've shown the PIR cut at an angle so as to keep the 200mm thickness as far as possible, but oversailing onto the EPS inner skin of the Nudura.

 

Of course I realise I'd have to place firrings under the Plywood for the fall.

 

Keep in mind there is an outer unifying 50mm skin of EPS to go on in addition to that drawn, this will cover the external timbers. What width should the Parapet be? From the centreline of the Nudura outwards it would be roughly 200mm without needing that inward overhang and might allow the PIR to oversail a bit more.

 

We would run the EPDM up the adjoining walls of the two-storey building.

 

If the Parapet can be kept to 250mm maximum as denoted, it would leave 80-100mm underneath the structural opening of the window. Also, depending on what height the Parapet would need to be in relation to the insulation and gutter depth, it might not even need to be as funky as I've drawn it.

 

@ETC - I would be very happy to pay your rates to do a proper detail drawing if you think a version of this/your idea could work.

 

 

Any good?

Edited June 18 by Mulberry View

[Dave Jones]

replace the window for a wider/narrower one to give you some height ?

 

Good example of an architect drawing being total crap when it comes to the reality of building.

[Mulberry View]

47 minutes ago, Dave Jones said:

replace the window for a wider/narrower one to give you some height ?

 

Good example of an architect drawing being total crap when it comes to the reality of building.

 

@Dave Jones With respect Dave, can you ease up on tearing holes in our design. I hate our Architect with a passion, but we're generally very happy with the overall design. I could do without anything else to feel negative about right now.

[Kelvin]

Is OSB the standard underbuild for EPDM? I’d be using exterior grade plywood. Our flat roof uses Alwitra Avalon VSK membrane on 18mm plywood. 
 

The cut in for the gutter in your picture would worry me. That shape Looks hard to detail correctly. Would it not be better to try and build it as a more straightforward L shape. 
 

 

Edited June 19 by Kelvin

[garrymartin]

17 minutes ago, Kelvin said:

Is OSB the standard underbuild for EPDM?

Not necessarily the standard, but it's acceptable.

 

I initially went for OSB on my garden room build but I wasn't happy with the variances in thickness from board to board considering I would be putting a nice flat EPDM membrane over them. Switched to exterior grade plywood.

[Mulberry View]

19 minutes ago, Kelvin said:

Is OSB the standard underbuild for EPDM? I’d be using exterior grade plywood. Our flat roof uses Alwitra Avalon VSK membrane on 18mm plywood. 
 

The cut in for the gutter in your picture would worry me. That shape Looks hard to detail correctly. Would it not be better to try and build it as a more straightforward L shape. 
 

 

 

Yes, OSB is what most seem to suggest as Plywood can apparently delaminate under a fully adhered membrane.

 

I agree, the way I've drawn it is off, but I'm trying to figure if the general principle works. Mainly in terms of the parapet wall height in relation to the insulation depth.

 

[Kelvin]

I’d try and use a specifically designed edge flashing where possible rather than try and use the membrane to make the water seal. 
 

Have a look here. There are loads of drawings showing how to detail different situations. This is for Alwitra obviously but the general principles will be the same. 
 

https://www.icb.uk.com/downloads/waterproofing-sdrawings

 

[Thorfun]

21 hours ago, Mulberry View said:

The rearmost window is not problematic, it's the front one. I only have 350mm from the top of the Posis in the flat roof section to the sill.

we had this situation. the window as designed would've been below the level of the green roof. we had to bite the bullet and purchase a new window and raise the wall to bring it up. but probably easier for us as ours was timber frame so i just built up the frame to the required level. we couldn't return the window that was too large so we cut a hole in a wall elsewhere and fitted it there. now we wouldn't even know it wasn't part of the original design!

[Thorfun]

39 minutes ago, Kelvin said:

Is OSB the standard underbuild for EPDM? I’d be using exterior grade plywood. Our flat roof uses Alwitra Avalon VSK membrane on 18mm plywood. 
 

The cut in for the gutter in your picture would worry me. That shape Looks hard to detail correctly. Would it not be better to try and build it as a more straightforward L shape. 
 

 

our roofers used OSB with the Alwitra VSK membrane.

[Mulberry View]

1 hour ago, Thorfun said:

we had this situation. the window as designed would've been below the level of the green roof. we had to bite the bullet and purchase a new window and raise the wall to bring it up. but probably easier for us as ours was timber frame so i just built up the frame to the required level. we couldn't return the window that was too large so we cut a hole in a wall elsewhere and fitted it there. now we wouldn't even know it wasn't part of the original design!

 

Crikey, that does sound like a similar situation. We haven't ordered the windows yet, but I'm reluctant to push the sill level up as it'll be my Grand-Daughters bedroom. I wanted her to have a low sill (I already had to raise it from 800mm to 900mm off the floor). If I have to I will, but it's a last resort.

 

Is the Alwitra VSK the gold standard for this type of coating?

[Russell griffiths]

Have you considered closed cell spray foam sprayed to the underside of the osb, whithin the webs of the posi joist

50mm pir on top of joist and 150 spray foam inbetween. 
 

very little height build up then. 
 

your box gutter shape needs changing to vertical sides, with no horizontal epdm stuck under that parapet. 

[Mulberry View]

6 minutes ago, Russell griffiths said:

Have you considered closed cell spray foam sprayed to the underside of the osb, whithin the webs of the posi joist

50mm pir on top of joist and 150 spray foam inbetween. 
 

very little height build up then. 
 

your box gutter shape needs changing to vertical sides, with no horizontal epdm stuck under that parapet. 

 

No I hadn't. I think I can accommodate insulation in the Posi area, but worry about the hybrid roof thing as this will be under the VCL.

 

I agree on the box gutter shape. I'll have a measure up today and see what I think I can do with having fully vertical sides. I'm just trying to get as much PIR as possible over the wall-roof junction as I imagine that's where potential bridging issues can arise?

[Kelvin]

27 minutes ago, Mulberry View said:

 

Is the Alwitra VSK the gold standard for this type of coating?

I don’t know about gold standard but it is a good product and commonly used under sedum roofs. It’s used a lot on big commercial roofs. Sarnafil is another similar product that’s more common around where I am as most of the flat roofs use it. Both can be applied direct to PIR. 

Edited June 19 by Kelvin

[Thorfun]

1 hour ago, Mulberry View said:

 

Crikey, that does sound like a similar situation. We haven't ordered the windows yet, but I'm reluctant to push the sill level up as it'll be my Grand-Daughters bedroom. I wanted her to have a low sill (I already had to raise it from 800mm to 900mm off the floor). If I have to I will, but it's a last resort.

 

Is the Alwitra VSK the gold standard for this type of coating?

ahh...ok so yeah i understand not wanting to raise it further! ours was a floor level window so raising it 300mm or so wasn't a big deal.

 

our roofer recommended the Alwitra solution and he raved about it. for me, i got a 25yr insurance backed guarantee so that was good enough for me! happy to let someone else make that decision for me as i had plenty others to focus on

[Thorfun]

1 hour ago, Mulberry View said:

 

No I hadn't. I think I can accommodate insulation in the Posi area, but worry about the hybrid roof thing as this will be under the VCL.

 

I agree on the box gutter shape. I'll have a measure up today and see what I think I can do with having fully vertical sides. I'm just trying to get as much PIR as possible over the wall-roof junction as I imagine that's where potential bridging issues can arise?

we also had a balcony that was causing issues with height and finished floor level. the architect's solution was a hybrid roof in that area. we had an interstitial condensation analysis done and it was ok. it was the only way to get a decent level of insulation.

 

initially they'd specified vacuum sealed insulation panels but they're stupidly expensive and very hard to work with. so the hybrid solution was cheaper and gave similar levels of insulation.