Thermal bridge of vertical metalwork

[MattMiller]

Hi all,

I have an issue on an extension of a house I bought last year where a flat roof extension has been installed with two walls in large glass panels. This is for an ensuite and dressing room. There is a step in the longest glass wall that is also glass. This leaves 3 steel uprights at 3 corners. (no we are not overlooked and having a garden with trees all around leave you happily having a bath with the blinds open:) ). Issue is the flat roof and thermal bridging of the steel Columns. I expect that there is some steel work in the roof above the windows but there is no access to see other than a hole I cut to see what insulation is up there. And I expect the roof steel is also uninsulated. Answer to insulation, non that is doing any good, as it is not held in place and as it is board insulation its fallen down leaving air passage. And shoved between joists as a cold roof that  pointlessly holds insulation.  

 

The roof is covered with lead and is 9.3m by 7.5m slope is along the shortest side. There are no steps in the roof and joints are double lapped, incorrectly. Roof is OSB and is rotting as the laps of the lead is not covering enough. Short side is it needs to come off.

 

Regarding the thermal bridge on the upright steel, the windows are fitted directly to the steel poles... So the double glazing is pretty useless. We are looking to getting new windows and we need to insulate the poles as best as we can. What would be the best recommendation, minimum insulation thickness vs best thickness?  I am going to assume we can use a ridged board insulation and then should use some form of water proof covering over the top, I had thought of using the lead from the roof in some fashion, but how best should I construct the covering to provide a good seal for the new windows?

The roof is a totally different issue, as height is a problem and the only flow of air will be back into the main roof of the house which I expect will not be the best airflow for a cold insulation, as the beams used are small, I think only 150mm possibly 100mm.  There are small soffit vents approx 70mm. 

 

We are thinking of replacing with a warm roof, however due to a vellux window there is a height restriction, also there is a raised Velux in the middle of the flat roof. If there is a suitable solution for a cold roof we may consider that. The final covering will likely be EPDM as the cost of led work and required height raise of 225 to account for the required steps is not possible due to the vellux. If we keep the insulation to max 150mm we should be able to avoid the window..

 

I hope to do the work other than the EPDM myself, simply due to cost, so material guidance is also sought after, so far thought is 18mm exterior WBP ply. Alutrix 600 barrier. 120 Kingspan, or if anyone can recommend better/ cheaper, then EPDM. I would have liked a hard covering on the insulation as we have over hanging trees, but according to timber development uk this is no longer recommended as the EDPM will trap moisture between the vapour barrier and wood will rot? Someone please tell me if I'm wrong as this is all my own research so not 100%

 

I will put some photos up tomorrow so folks can see. 

 

Many thanks, Matt

[Conor]

Any pics?

 

Tbh, it sounds like you'd be best ripping the whole thing down and starting again. You'll get a good bit of cash for the lead roof at least.

 

The roof sounds like a disaster and needs redoing.

 

The heatloss by the steel posts is probably nothing compared to what you're losing through the old double glazing. Even if you replace with triple glazed units, this will still be significant. Consider a proper redesign the reduces the heatloss.

 

Re the corner posts. The best way is to position these behind the galzing units. I.e. right inside and the frames of the units meet to the outside. So they are not forming and kind of bridge. See attached.

 

This doesn't always work due to boring structural reasons. For us, we couldn't do this and the compromise was to set the post at the inner join of the two frames. So we had the depth of the frames (50mm) between the post and outside world. We put in 50mm PIR with foil tape, and the window company made an aluminium flashing that covers the whole lot. On the inside, I wrapped the post in aerogel before boarding.

[JohnMo]

That's pretty much how our windows where done on our steel frame.  The internal surfaces of the steel had 10mm aerogel and PIR basically because the steels go down to the foundations and it stops the ground temp being transferred to the room.

[MattMiller]

so photos below of the area. the bathroom is all glass with the steel work as described at the corners. And the dressing room is similar. the steel work is internal and external so placing the windows around them would mean increasing the size of the extension and no doubt planning permission. photos of inside the roof space are as poor as they seem. 

 

ripping down and starting again would be ideal but we just don't have the ready funds for that

[MattMiller]

@JohnMo what you say thats how your steel work was done do you mean the same as mine or @connor described?

[PeterW]

22 hours ago, MattMiller said:

as the beams used are small, I think only 150mm possibly 100mm. 

That can’t be right ..??!! A 70sqm lead roof will weigh over 1.7 tonnes and the max span on a 100mm joist is less than 2m. 
 

22 hours ago, MattMiller said:

thought is 18mm exterior WBP ply. Alutrix 600 barrier. 120 Kingspan, or if anyone can recommend better/ cheaper, then EPDM. I would have liked a hard covering on the insulation as we have over hanging trees,

 
That’s fine - and standard build up is adding 11mm OSB to the top and screwing through into the ply through the insulation then add the EPDM. 

At current scrap price of £1.62/kg then your roof is worth about £2700 so will

easily cover the cost of a good chunk of the replacement roof !

 

[Nickfromwales]

Where's the extraction for the 'bathroom', and vapour barrier? Those look to be regular plasterboards.

 

The metal posts can be clad with either Compacfoam ( 20mm minimum thickness ) or Marmox insulated boards ( 6mm minimum thickness ). The new windows can be made smaller to fit up against these products.

[Radian]

58 minutes ago, Nickfromwales said:

Where's the extraction for the 'bathroom', and vapour barrier? Those look to be regular plasterboards.

 

It's a sobering lesson for anyone not understanding what interstitial condensation is all about. Downlighters, no vapour barrier, poor insulation. No doubt it all looked fabulous the day it was done but the consequences would soon begin to reveal themselves and the whole thing probably became a constant worry for the original owner. Looks like   @MattMiller 's gonna sort it out 😃

[JohnMo]

 

11 hours ago, MattMiller said:

@JohnMo what you say thats how your steel work was done do you mean the same as mine or @connor described?

Same as @Conor

[Nickfromwales]

40 minutes ago, Radian said:

It's a sobering lesson for anyone not understanding what interstitial condensation is all about. Downlighters, no vapour barrier, poor insulation. No doubt it all looked fabulous the day it was done but the consequences would soon begin to reveal themselves and the whole thing probably became a constant worry for the original owner. Looks like   @MattMiller 's gonna sort it out 😃

Worse still is the builder who dutifully patted himself on the back and congratulated himself on a job well done. And a fortunes worth of lead laid onto a ticking time-bomb.

I shudder to think about a nice steaming hot bath in there whilst there is a bit of frost / snow on the lead.....ouch.

 

@MattMiller

Are you 100% sure the roof is actually leaking? The interstitial condensation issues here must be off the chart. Could it be vapour collecting, condensing and then running down?

[Iceverge]

@MattMiller

 

It sounds like a whole chunk of heartache.  

 

What will your budget allow? Can you provide any pics of the outside structure etc? 

 

In the short term I would get a dehumidifiers and let it in there 24/7 and stop bathing/showering too if possible. You need to stop putting any more moisture into the structure ASAP.  

 

What kind of ceiling height do you have to play with internally? Maybe there's a cheaper solution than stripping the roof and starting from scratch. 

[MJNewton]

I'm amazed an extension like that was able to get through building regs given the amount of glazing. Presumably it takes an awful lot of heating to keep it comfortable?

 

Is the roof definitely not of warm construction? I know you/we can see some insulation on the underside but I was just wondering if this was perhaps thrown in for extra measure (a token gesture at that) and that there's a decent amount above the OSB too (making something of a hybrid construction)?

 

As others have mentioned I'd be interested in seeing some outside pics too.

Edited January 9, 2023 by MJNewton

[MattMiller]

Hi guys. 

 

first off thanks for the help. Second sorry for the delay. I have been having Window quotes done. 

Everest 25k

Anglian 15k

Local 12k

I will get a heap of photos tomorrow. 

Roof depth is 300mm joists 150mm length of roof 9.3m slope or width of roof 7.5m.

Interior height 2.4m 

Plasterboard I think is generic.

Ventilation fan in bathroom is tiney so have a 150mm manrose to go in. 

Haven't used this bathroom in winter and roof leaks only in severe weather. 

Terribly wet osb. 

Dont think I can warm roof Insulate as the main roof has a velux in it and is only about 100mm from the top of the lead roof. 

There is also a raised velus in the lead roof.

 

Thought here is

Raise joists by 50mm battens. 

Put 100mm hard insulation ( please recommend brand for me) between the joists. Leave an air space of 50mm. 

18mm marine grade ply or would I be better with grade 3 osb or grade 4 On the cold side of the joists

the rubber onto that

No capture barrier on this one... or where would I put it for a cold roof?

 

Or 

18mm marine ply on joists

Altrix 600 or another vapour barrier ( please recomend)

50mm hard insulation on ply

11mm osb 3? Or 4? 

the the EPDM?

 

can i put more insulation between the beams with air gap to underside of the play or is it worthless? 

 

currently there are air belts as its a cold roof so I guess on a warm roof I would seal those off? 

 

yes having to do this myself... roofer with led 15k 

roofer with rubber 13k 

Windows 15 to 25k

i dont have that ... simples. 

Photos to follow in detail tomorrow

 

[MattMiller]

On 08/01/2023 at 09:47, JohnMo said:

That's pretty much how our windows where done on our steel frame.  The internal surfaces of the steel had 10mm aerogel and PIR basically because the steels go down to the foundations and it stops the ground temp being transferred to the room.

 

On 09/01/2023 at 10:46, MJNewton said:

I'm amazed an extension like that was able to get through building regs given the amount of glazing. Presumably it takes an awful lot of heating to keep it comfortable?

 

Is the roof definitely not of warm construction? I know you/we can see some insulation on the underside but I was just wondering if this was perhaps thrown in for extra measure (a token gesture at that) and that there's a decent amount above the OSB too (making something of a hybrid construction)?

 

As others have mentioned I'd be interested in seeing some outside pics too.

 

So attached below are the outside photos. 

@MJNewton it is baltic in here. glass to the touch is icy cold so the glazing is shot. ironically Everest glazing and dated 2007, but as everest went into receivership 2020, apparently due to covid, i laugh, and reopened as Everest 2020 limited, they no longer honour their 20 year warranty on glazed units... so your warranty is worth hehaw.

Grey posts at the corners are the steel supports as seen inside the room. so no insulation at all on those. 

the roof cavity is at a guess from sticking my head in the hole 150mm no more at the edge of the building and the cavity increases to the house side to 250 potentially 350 at a guess. not enough to really crawl in. 

Plasterboard is your standard paper backed. no foil backed or water resistant at all. and same in the bathroom. 

 

I guess my questions here are, 

 

To replace the roof do i need building inspections

do i need to get planning permission?

can i change the positioning of the windows under the roof without needing to get planning? if i decide to go inside the poles or outside.

 

issue moving either way is the wall is in line with the outside of the pole so moving either way i would have to build to the outside of the wall or inside into the room. 

 

@Iceverge standard height room 2.4m

@Nickfromwales without sounding like the churchill dog Oh yes, only happens under bad weather from west or north

 

@Radian what is your suggestion on correct plasterboard type, and vapour barrier. as i'm going to have to do this one myself as getting outcosted with requirement for new windows and roof.

 

@PeterW are you able to advise on the exspance fro 150mm joist, luckly but possibly not, there are walls within the roof space, there is the bathroom, dressing room and a laundry room so internal walls in a T shape as well as a large cupboard. I have no idea how and if the walls are acting correctly as a supporting wall.

 

@Conor @JohnMo and @ anyone else how would i correct these mistakes. as best i can. I am an able bodied person with DIY and much more so happy to take it all on.

 

Any advise on building regs in scotland would help too, inc need for planning. and anyone done a rubber roof able to give pointers on the skylight velux as well? brands of products inc insulation rubber and glues as well as vapour barriers please give an opinion. 

 

looking to start in april or march

[MattMiller]

some more images inside and a sketch with sizes in meters.

[MattMiller]

The photo with my hand is indicating about 100mm that there is potential to warm roof insulate, but that would include the 11mm osb and rubber.

 

on the sketch the chevron is not part of the house. 

 

BIG thanks to everyone on this. Nice community to help folk.

Edited January 21, 2023 by MattMiller

[Iceverge]

That's a tremendous amount of info. Well done. Will go through it later. 

[HughF]

What an interesting (read, weird) extension... personally I'd go full planning, knock it down and rebuild the floorplan in proper construction to match the original house.

 

Steel frame/glass infill has it's place - in the city

Edited January 21, 2023 by HughF

[MattMiller]

@HughF , I would agree however cost is out of my possibility right now. With a wee baby we just need it warmer and no damp. 

Cheaper in the long run but just cant manage it right now. 

 

The old house is 3ft thick stone walls, so there is no likely hood of passing building regs on that. 

Does anyone have any idea on how building regs work in Scotland as internet searches only shows up for England, and Right now I have no idea if I need to inform local authorities in order to change the roof from lead to rubber or anything else. 

 

I read that England requires a flat roof to fall under new insulation building regs if replacing more than 25% of it.... 

[Radian]

59 minutes ago, MattMiller said:

The old house is 3ft thick stone walls

That comes as a bit of a surprise. May I ask if the house is detached or semi-detached? Trying to understand the overall footprint. Looks to be in a lovely location!

[MattMiller]

5 hours ago, Radian said:

That comes as a bit of a surprise. May I ask if the house is detached or semi-detached? Trying to understand the overall footprint. Looks to be in a lovely location!

Old stone farm cottage , single story, fully detached, thanks it is in the country with fields and surrounded by trees on the fence line. love it here.

 

[MattMiller]

the extension with ensuit and dressing room is a block brick wall only 300 ish  thick

 

 

[Iceverge]

Congratulations on the newborn. It's a special time, and the house. Also having ones own home is something to celebrate, even when it needs improvement. 

 

I have been studying this and making assumptions...….

 

1. You like the house and the area.

2. It is sufficient in size and layout for your needs. 

3. A budget for a knock and rebuild is completely off the table?

4. It suffers from poor ventilation.

5. You have lots of drafts, lots of outside doors, lots of sliding patio doors. (Notoriously draughty) 

6. The house has awful thermal bridging, especially the extension with all the steelwork etc. 

7. You are relatively confident regarding DIY etc

8. You need to live in the house whilst any work is ongoing. 

9. The house swallows heat like there is no tomorrow given it's large outside surface area vs internal area. (form factor)

10. You need to live in the house whilst any work is ongoing.

11. You will be able to afford over a few years to get it to a good standard. Just not in one go. 

12. You're off the mains gas network?

 

 

 

I don't know much about Bregs, especially in Scotland. However in practice it's unlightly anybody will stop you. Tell the neighbours how bad it is, with the baby etc and they'll be lightly to support you rather than call the council. 

 

Here is my proposed list of actions. 

 

1. That flat roof has to go.  Take it down and scrap the lead. Erect a proper pitched roof integrated into the original house. Assuming you have at least 10 deg pitch you can use roof tiles which are cheap and durable. Leave at least 600mm overhang at the gables/eves.  Insulate it all with 400mm+ of insulation. Rolls of mineral wool are cheapest but a blown one like cellulose or Glass Mineral Blowing Wool will be easier to fit and re settle when you put in ducting, pipes and wires at a later date. 

 

2. When budget allows strip the original roof and with a bell cast extend the eaves and gables at least 600mm also. 

 

3. When the money allows for new windows and external insulation go ahead and do this, You can do one wall at a time if budget is constrained. Take the insulation around the outside of the steel poles and existing stone walls. You can continue living in the house while this goes on. Install the new windows in the insulation layer. Good quality PVC are fine, compression seals are vastly superior to brush seals so avoid patio doors, bifolds and sash windows. 

 

4. Install some kind of ventilation system that draws air out of all wet rooms continuously and vents it outside. This can be done now, a decent inline fan, a silencer and some ducting would be enough to get you started for a few £100. 

 

 

The only really disruptive part of this is taking the roof off. Everything else can be done bit by bit and without upsetting the apple cart inside. Important with a family there. 

You could even use the opportunity of external insulation to really spruce up the outside, metal wood cladding etc. 

 

 

 

 

 

 

 

[Radian]

1 hour ago, MattMiller said:

Old stone farm cottage , single story, fully detached, thanks it is in the country with fields and surrounded by trees on the fence line. love it here.

 

Superb! I agree with everything @Iceverge says above. Only I'm not sure you've got enough ridge height to create a pitched roof. Really does need some careful consideration because it would be transformative if it could be accomplished.

[MattMiller]

Wow, what an explanation @Iceverge. Thanks man, and you are right, my daughter and fiancé are my life and I never thought I would have kids. I guess 40 isn't too late to find someone that's right for you! And I could never have dreamed of having a house like this, incredibly lucky to have bought a house cheaply in a good area a few years back and the prices rocketed because of it being in a desirable school area. Then meeting the other half who had done similarly. 

 

So in answer to your points:

 

1. You like the house and the area. Absolutely, We bought the house in March 2022, it is a dream. Location is almost at the top of a low lying hill but 2 fields from a light aircraft landing field. Not noisy so not a concern. however it is mighty windy. 

2. It is sufficient in size and layout for your needs. I moved from a 800sqm house to over 2600sqm so yes we have space for the three of us!

3. A budget for a knock and rebuild is completely off the table? At the moment the extension is only a en-suit, dressing room, with laundry and cupboard, we don't need it to be glorious, but we do need to improve the icy cold in there.

4. It suffers from poor ventilation. I have a manrose MF150T to go in. enough draw to inflate a hot air balloon. 

5. You have lots of drafts, lots of outside doors, lots of sliding patio doors. (Notoriously draughty) Main bedroom is patio sliding door, its going to go and become a French door, We have the orange shutter door between the bedroom and bathroom and shutters over the bedroom door as well. the glass in the en-suit and dressing room i think is less then half the cold issue, the uninsulated roof is the pain. 

6. The house has awful thermal bridging, especially the extension with all the steelwork etc. the structural poles, are literally acting as air-conditioning units on lower than low, with the wind blowing past them they are drawing the heat out of the place. 

7. You are relatively confident regarding DIY etc I fully stripped out my last house and redid plumbing, kitchen bathroom, some wiring and had it certified, so happy enough. also a mechanical Engineer in oil and gas so yea im confident i can do most things.

8. You need to live in the house whilst any work is ongoing. Yes, there is a  main bathroom so the dressing room and En-suit can be out of action for as long as needed.

9. The house swallows heat like there is no tomorrow given it's large outside surface area vs internal area. (form factor) 100%, especially the extension. Main house with stone walls actually retains the heat well. 

10. You need to live in the house whilst any work is ongoing. Yup

11. You will be able to afford over a few years to get it to a good standard. Just not in one go. Yup

12. You're off the mains gas network? No mains gas or sewage. we have gas only for the kitchen hobs, and a septic tank.  Solar on the roof, intention is to get more and batter storage independent of the main house so as not to affect the feed in tariff.

 

I don't know much about Bregs, especially in Scotland. However in practice it's unlikely anybody will stop you. Tell the neighbours how bad it is, with the baby etc and they'll be lightly to support you rather than call the council.  The neighbours are 3 fields away and we are surrounded by a fence line of 200 year old trees. i dont have a clue where to start with who i need to speak to regarding planning other than the council

 

 

1. That flat roof has to go.  Take it down and scrap the lead. Erect a proper pitched roof integrated into the original house. Do you mean to the same height as the main house roof? What would be the benefit of adding this?

Assuming you have at least 10 deg pitch you can use roof tiles which are cheap and durable. 8% at most currently and we have a velux in the main house roof over the top of the flat roof to give light to a rather dark hall way. we would need to account for this in a full pitched roof. and cost I have no idea what this would be.  Max i could rais the roof to the house side would be 100mm.  which should give a greater % run off.

Leave at least 600mm overhang at the gables/eves.  Insulate it all with 400mm+ of insulation. Rolls of mineral wool are cheapest but a blown one like cellulose or Glass Mineral Blowing Wool will be easier to fit and re settle when you put in ducting, pipes and wires at a later date. Would hard insulation be better, I would rather spend more for something better if we are retaining the flat roof... 

 

2. When budget allows strip the original roof and with a bell cast extend the eaves and gables at least 600mm also. Sorry, I'm no building expert, what is a bell cast? 

 

3. When the money allows for new windows and external insulation go ahead and do this, You can do one wall at a time if budget is constrained. Take the insulation around the outside of the steel poles and existing stone walls. You can continue living in the house while this goes on. Install the new windows in the insulation layer.

I guess I have to ask, will I need planning for this? I assume I use external hard insulation and then roughcast onto that.  W cannot insulate the stone part of the house externally as far as I know, it would dry out the stone too much and stop the house breathing. I know I can insulate internally with a fibrous board and lime plaster render though as I helped family do this to their home. 

Good quality PVC are fine, compression seals are vastly superior to brush seals so avoid patio doors, bifolds and sash windows.  Absolutely

 

4. Install some kind of ventilation system that draws air out of all wet rooms continuously and vents it outside. This can be done now, a decent inline fan, a silencer and some ducting would be enough to get you started for a few £100.  Only thing I'm certain about, Ha ha

 

link to the house to give you a better idea of it all 

https://www.facebook.com/ResidenceEstateAgents/posts/6613161455421700/