Converting wooden workshop to office

[Adthrawn]

[Adthrawn]

[Adthrawn]

Knot exposing the polysheeting.

[Adthrawn]

[SteamyTea]

6 hours ago, Adthrawn said:

To what degree would that change the wall buildups?

Just becomes a standard wall makeup.

So apart from plasterboard, everything is outboard of the VCL and gets more vapour open as you travel outwards.

[Adthrawn]

1 hour ago, SteamyTea said:

Just becomes a standard wall makeup.

So apart from plasterboard, everything is outboard of the VCL and gets more vapour open as you travel outwards.

Okay, so would require removal of the old poly sheeting (it’s under the cladding at the very outer)?

 

or would high level vents that cut through the poly be sufficient?

 

I wouldn’t have to remove all of the cladding - I could even maybe get away with removing internal plywood as well to remove the poly if needed. 

Edited May 30, 2022 by Adthrawn

[Adthrawn]

14 hours ago, Iceverge said:

Can you cancel the materials?!

 

PIR is expensive and not suitable for anything other than floor insulation in my opinion. 

 

I’ve cancelled them…

 

will still get some PIR for the floor (50mm). Still deciding on finished floor - would have liked an amtico etc, but  need floating flooring. That said, if I put double lapped OSB down, is that secured in anyway and suitable for adhered floors, or is that still left as a floating floor?

 

anyway, I’ll build an internal stud frame now. Still need to figure out the external poly sheeting under the cladding. With a new stud frame, I’m guessing okay to tie it to the plywood; there’s no issues with damp etc? I’ll probably put a poly sheet under plasterboard, unless I can foil tape the uprights and silicon seal as they go on etc. 

[SteamyTea]

19 minutes ago, Adthrawn said:

Okay, so would require removal of the old poly sheeting (it’s under the cladding at the very outer)?

I assume this is the rain screen, so should be ventilated and allow any liquid water to escape from the bottom.

 

The idea, in the UK climate, is that humidity and temperatures are higher on the inside of the building.  The insulation makeup, once past the VCL, is to allow water vapour to escape and evaporate.  The living area is treated differently as that is usually serviced with natural, or forced ventilation, this reduces the amount of water vapour that can enter into the wall build up.

Wind driven rain is stopped by cladding, and/or, an extra layer of liquid water impervious sheeting, but needs a gap between itself and the main structure.  It effectively adds nothing to the insulation levels as air can easily travel behind it.

Wind is stopped by the airtight barrier, on the outside of the structure, but before the air gap and cladding.

[Adthrawn]

38 minutes ago, SteamyTea said:

I assume this is the rain screen, so should be ventilated and allow any liquid water to escape from the bottom.

 

The idea, in the UK climate, is that humidity and temperatures are higher on the inside of the building.  The insulation makeup, once past the VCL, is to allow water vapour to escape and evaporate.  The living area is treated differently as that is usually serviced with natural, or forced ventilation, this reduces the amount of water vapour that can enter into the wall build up.

Wind driven rain is stopped by cladding, and/or, an extra layer of liquid water impervious sheeting, but needs a gap between itself and the main structure.  It effectively adds nothing to the insulation levels as air can easily travel behind it.

Wind is stopped by the airtight barrier, on the outside of the structure, but before the air gap and cladding.

 

I'm not sure how it's been fitted, whether it wraps under the frame or not. I'm hoping it's "loose" at the base, but it'll still be held against the bottom of the frame by the cladding. The poly is very much not a breathable moisture sheet. There's no ventilation in the panels, so the poly seems to have been fitted as a water barrier without consideration of condensate/ventilation.

 

It's fairly lightly filled with a fibre glass insulation of some kind. So, to add ventilation, it should be an easy job of cutting a 60-80mm hole in the top of each void and putting a vent.

 

43 minutes ago, SteamyTea said:

Wind is stopped by the airtight barrier, on the outside of the structure, but before the air gap and cladding.

 

Do you mean the poly sheet under the cladding or when the plywood skin is taped up and that'll be an airtight barrier?

[SteamyTea]

3 minutes ago, Adthrawn said:

 

I'm not sure how it's been fitted, whether it wraps under the frame or not. I'm hoping it's "loose" at the base, but it'll still be held against the bottom of the frame by the cladding. The poly is very much not a breathable moisture sheet. There's no ventilation in the panels, so the poly seems to have been fitted as a water barrier without consideration of condensate/ventilation.

 

It's fairly lightly filled with a fibre glass insulation of some kind. So, to add ventilation, it should be an easy job of cutting a 60-80mm hole in the top of each void and putting a vent.

 

 

Do you mean the poly sheet under the cladding or when the plywood skin is taped up and that'll be an airtight barrier?

Yes. It is probably there as a secondary rain screen.

 

There is some confusion about wall buildups because, in the USA, they frequently do the opposite to us. This is because they air condition their homes and the outside air is hot and humid. Some say that we need to treat sheds the same as they are unheated and our external air has high humidity.

But as soon as it becomes a heated area, then water vapour needs to escape. This is why the most vapour resistant later us on the inside and each additional layer is less resistant.

Not too much of a real problem when the recommended airchanges and working temperatures are well controlled.

[Adthrawn]

20 minutes ago, SteamyTea said:

Yes. It is probably there as a secondary rain screen.

 

There is some confusion about wall buildups because, in the USA, they frequently do the opposite to us. This is because they air condition their homes and the outside air is hot and humid. Some say that we need to treat sheds the same as they are unheated and our external air has high humidity.

But as soon as it becomes a heated area, then water vapour needs to escape. This is why the most vapour resistant later us on the inside and each additional layer is less resistant.

Not too much of a real problem when the recommended airchanges and working temperatures are well controlled.

Okay, so adding vents to the top of the cladding should alleviate any moisture on the outside layers. I'll be putting a heat exchanger of some kind for ventilation - we need the fresh air through, and want to retain the heat.

[SteamyTea]

Just now, Adthrawn said:

, so adding vents to the top of the cladding should alleviate any moisture on the outside layers

Should do. Just make sure wind blown rain is not a problem.

And some small drain holes at the base for any liquid water.

[Iceverge]

Most of the cladding looks to be in good order, as does the roof. Leave well enough alone I say. 

 

What are you planning on doing with the windows/doors?

 

 

 

One area that might merit some thought would be the bottom run of cladding. It looks like it is suffering from some splashback from rainwater ( red looped areas) .  Normally cladding wouldn't start 150-200mm above the ground to prevent this. 

 

 

 

 

A simple solution might be to cut the concrete along the blue line maybe up to 300-400mm back from the wall, with one of these.

You could break it by hand but it wouldn't be as neat. 

 

Then dig out 300mm deep and backfill with 100-150mm of gravel. This should be enough to ensure the timber stays dry. 

 

 

What is your plan for the electrics? 

 

If the internal ply hasn't rotted with the poly/paint sandwich by now it's not going to. 

 

Get some airtightness tape and tape all the joints in the plywood and tape the doors and windows to the ply. Tape the ply to the roof and floor making a perfectly airtight box. This is more important than insulation in creating a stable internal environment.  Very easy to DIY, just takes care. 

 

 

For the walls I'd use 63mm CLS set back from the wall by 38mm @600 c/c. Any smaller timber will be too bendy to get a nice wall finish. You can use a 38*63mm CLS timber on its side screwed through the ply tot he studs at the top ( and bottom if required) to create this setback . 

 

This will create a 100mm ish (63mm+38mm) space to fill with 600mm rockwool batts or similar. Also the gap behind the studs will give you a nice thermal break and leave a gap for the electric cables etc. Then cover with 15mm plasterboard. 

 

 

2 hours ago, Adthrawn said:

Still deciding on finished floor - would have liked an amtico etc, but  need floating flooring. That said, if I put double lapped OSB down, is that secured in anyway and suitable for adhered floors, or is that still left as a floating floor?

 

If you glue the two layers or OSB together with all joints well staggered and stick down the Amtico too it'll work fine. I'm not an expert but I can't see any issues. You'll need to get your floor insulation dead flat first however. If the floor of your shed is undulating use a straight edge and some sand/cement mix or tile adhesive to fill any low spots.  Put down your insulation and the OSB on top. make sure to leave a few mm for the OSB to expand at the edge. 

 

For ventilation I'd use something like this and a trickle vent in the opposite wall .

 

 

 

 

OR if you want to splash out something like this, 

 

 

 

For heating I think in a small space, the heat of the printers and humans will make even a cheap air2air heat pump unnecessary. A simple plug in rad will be fine. 

 

 

 

Sorry for the scattered post. Hope it makes sense. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Edited May 30, 2022 by Iceverge

[Adthrawn]

9 hours ago, Iceverge said:

Most of the cladding looks to be in good order, as does the roof. Leave well enough alone I say. 

 

What are you planning on doing with the windows/doors?

 

 

 

One area that might merit some thought would be the bottom run of cladding. It looks like it is suffering from some splashback from rainwater ( red looped areas) .  Normally cladding wouldn't start 150-200mm above the ground to prevent this. 

 

 

 

 

A simple solution might be to cut the concrete along the blue line maybe up to 300-400mm back from the wall, with one of these.

You could break it by hand but it wouldn't be as neat. 

 

Then dig out 300mm deep and backfill with 100-150mm of gravel. This should be enough to ensure the timber stays dry. 

 

 

What is your plan for the electrics? 

 

If the internal ply hasn't rotted with the poly/paint sandwich by now it's not going to. 

 

Get some airtightness tape and tape all the joints in the plywood and tape the doors and windows to the ply. Tape the ply to the roof and floor making a perfectly airtight box. This is more important than insulation in creating a stable internal environment.  Very easy to DIY, just takes care. 

 

 

For the walls I'd use 63mm CLS set back from the wall by 38mm @600 c/c. Any smaller timber will be too bendy to get a nice wall finish. You can use a 38*63mm CLS timber on its side screwed through the ply tot he studs at the top ( and bottom if required) to create this setback . 

 

This will create a 100mm ish (63mm+38mm) space to fill with 600mm rockwool batts or similar. Also the gap behind the studs will give you a nice thermal break and leave a gap for the electric cables etc. Then cover with 15mm plasterboard. 

 

 

 

If you glue the two layers or OSB together with all joints well staggered and stick down the Amtico too it'll work fine. I'm not an expert but I can't see any issues. You'll need to get your floor insulation dead flat first however. If the floor of your shed is undulating use a straight edge and some sand/cement mix or tile adhesive to fill any low spots.  Put down your insulation and the OSB on top. make sure to leave a few mm for the OSB to expand at the edge. 

 

For ventilation I'd use something like this and a trickle vent in the opposite wall .

 

 

 

 

OR if you want to splash out something like this, 

 

 

 

For heating I think in a small space, the heat of the printers and humans will make even a cheap air2air heat pump unnecessary. A simple plug in rad will be fine. 

 

 

 

Sorry for the scattered post. Hope it makes sense. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Thank you for the detailed reply!

 

1A) Windows - the two side windows will be removed in the next phase. The neighbouring wooden garage is in a very poor state, so I'll pull that down and rebuild it. Longer lead time as will need planning, as want to change the roof direction for solar panels, and absorb space taken by other wooden "things" that have been built around it. The plan is to join the two buildings by a wide link, that will be both a passage and storage etc. This will take in the two Windows (single glazed and not very useful).

 

1B) Doors - replacing them with a 3-door bifold. Obviously wider opening needed, and that will be closer to the left-hand wall. The front wall appears to have been made from three "modules", so I'll have to rebuild some of the framework, but less of a job thanks to how the front has been built. I still need to source a threshold for the bifold, as want to account for the increase in floor thickness (circa 70mm with the 50mm PIR and 2x 9mm OSB (for amtico or less if a floating laminate flooring).

 

2) French gutter at front - totally agree with that, and around the sides and rear it's soil and been overgrown, so will scrape back soil but soil membrane down and put gravel down. Planning to leave the gravel until after building work, but if I'm just doing the inside now, then could be a "quick" job to get done first (already spent a couple of days clearing the overgrown ivy and weeds etc). The front path however will have to wait for the electrics...

 

3) Electrics - quite my forte, was planning to surface mount, but if I have a void, may as well hide the cabling and create a nice crisp white box... Linked to the above, the current power supply is an armoured cable buried in concrete. Not to my liking, and makes changing the path near impossible. I've already laid ducting along a fresh route, so when I pull the new cable in, I'll be free to cut the concrete in front.

 

4A) Ply sandwich - fair point, it's been standing for 15 years or so. Internal ventilation is definitely the big issue, as when I cleared out the old workbenches, shelving etc, the majority of the musty smell went. Still not completely gone, but a good bleaching of surfaces and properly ventilating the place should get rid of that.

 

4B) Air tight tape - just any foil tape, or something specific? Also, if taping the plywood, does this in effect become a vapour barrier? Is the insulated stud wall on the cold side or the warm side? Are you for/against the addition of ventilation in the top of the cladding panels? 

 

5) The stud wall does seem the best option, and something I can chip away at progressively... Because it's a metal roof (insulated panels), is there any special treatment of the top of the frame, like extending a tape or barrier between the frame/plasterboard and the plywood? I'll use skirting and trim at the roof to finish the plasterboard off. Or is the frame/plasterboard happy to just butt against the roof as-is?

 

6) I plan to lay a vapour barrier poly sheet under the PIR - I'm not sure if a barrier was laid in the concrete floor originally. I'll seal that to the plywood walls as well - would that be a sufficient DPC for the stud wall?

 

Thanks

Jon

[Iceverge]

12 hours ago, Adthrawn said:

1A) Windows - the two side windows will be removed in the next phase. The neighbouring wooden garage is in a very poor state, so I'll pull that down and rebuild it. Longer lead time as will need planning, as want to change the roof direction for solar panels, and absorb space taken by other wooden "things" that have been built around it. The plan is to join the two buildings by a wide link, that will be both a passage and storage etc. This will take in the two Windows (single glazed and not very useful).

 

As that might be a time off I'd treat the windows as if they were staying put for the time being, Tape into place and do your best to make sure they seal properly. 

 

12 hours ago, Adthrawn said:

1B) Doors - replacing them with a 3-door bifold. Obviously wider opening needed, and that will be closer to the left-hand wall. The front wall appears to have been made from three "modules", so I'll have to rebuild some of the framework, but less of a job thanks to how the front has been built. I still need to source a threshold for the bifold, as want to account for the increase in floor thickness (circa 70mm with the 50mm PIR and 2x 9mm OSB (for amtico or less if a floating laminate flooring).

 

 

This might be lots of work for limited benefit. The existing opening looks to be about 1800mm wide. I would put in a pair of French doors at half the price of bifolds into the existing opening. Bifolds are notoriously drafty unless you get very good ones. I wouldn't sweat too much about  the threshold. Door suppliers do PVC spacers that would raise your door to floor level. 

 

12 hours ago, Adthrawn said:

 

4B) Air tight tape - just any foil tape, or something specific? Also, if taping the plywood, does this in effect become a vapour barrier? Is the insulated stud wall on the cold side or the warm side? Are you for/against the addition of ventilation in the top of the cladding panels? 

 

So long as it is proper airtight tape I wouldn't be too fussy.  Something like this would work fine. 

https://passivehousesystems.co.uk/product/phs-argo-joint-tape/

Split tape is better for the windows.

https://passivehousesystems.co.uk/product/phs-85-15-split-release-tape/

 

I don't think ventilation will be needed, probably enough as is between he cladding boards, if they were going to rot they'd be well on their way at this stage. 

 

12 hours ago, Adthrawn said:

5) The stud wall does seem the best option, and something I can chip away at progressively... Because it's a metal roof (insulated panels), is there any special treatment of the top of the frame, like extending a tape or barrier between the frame/plasterboard and the plywood? I'll use skirting and trim at the roof to finish the plasterboard off. Or is the frame/plasterboard happy to just butt against the roof as-is?

 

I've been thinking about this, I would tape the joints between the panels and tape the panels to the plywood to complete your airtight box.  It's up to you how pretty you want it to look but you could batten a 22mm service cavity underneath and put a layer of plasterboard at the expense of some ceiling height. 

 

If you don't want to bother with this and are happy with a conduit running to the light fixtures I'd tape the edges of the  roof to the walls and use a white airtight sealant to seal the gaps between the panels. 

 

12 hours ago, Adthrawn said:

6) I plan to lay a vapour barrier poly sheet under the PIR - I'm not sure if a barrier was laid in the concrete floor originally. I'll seal that to the plywood walls as well - would that be a sufficient DPC for the stud wall?

 

This would be fine. 

[Adthrawn]

1 hour ago, Iceverge said:

I've been thinking about this, I would tape the joints between the panels and tape the panels to the plywood to complete your airtight box.  It's up to you how pretty you want it to look but you could batten a 22mm service cavity underneath and put a layer of plasterboard at the expense of some ceiling height. 

 

 

I was concerned about condensate - but might be the way forward. Are those panels okay to screw into for fitting battens too? And guess no insulation, just air void?

[Iceverge]

4 hours ago, Adthrawn said:

Are those panels okay to screw into for fitting battens too? And guess no insulation, just air void

 

 I can't see why not, I'd just use some 22*75 strapping but be careful not to over tighten the screws pulling them out of the metal skin.  Yup, air void is fine. 

[Adthrawn]

8 hours ago, Iceverge said:

So long as it is proper airtight tape I wouldn't be too fussy.  Something like this would work fine. 

https://passivehousesystems.co.uk/product/phs-argo-joint-tape/

Split tape is better for the windows.

https://passivehousesystems.co.uk/product/phs-85-15-split-release-tape/

Would an aluminium foil tape (everbuild etc) not be suitable, or do the PHS tapes perform differently?

[Iceverge]

It depends on the spec of that particular tape. I just picked a tape at random from google that was a specific A/T tape. 

 

You need something that will last the lifetime of the building.

 

There's a significant difference between off the shelf duct tape and dedicated airtight tape for example although to the eye they appear the same to begin with. 

 

Foil tape is probably fine provided the substrate is dry. Split tape is much easier on the windows however. 

[Adthrawn]

On 27/05/2022 at 18:46, Iceverge said:

Following the example of the States I don't think there's anything wrong with an air barrier external to the insulation provided the wall can dry to the inside and you do a top job on airtightness. In fact I think @IanR has an external airtightness layer, albeit with a breathable board outside. 

 

If the existing structure is ok I would avoid dismantling it, especially with kids and limited time. Building has a habit of taking 3 times longer than you expect. 

 

I would install the final windows and doors in the structure as is. Make your own blower door fan and make the external plywood totally sealed with tape at all the joints and to the floor. This isn't hard and is ideally suited to the DIY'er. Given it's your own project you're lightly to get a top result too.  

 

Then build a stand alone stud wall (63mm CLS minimum) stood off the ply internally by say 100mm. (can be increased/decreased) This will create a handy void for all your services. Fill this with mineral wool/ rockwool insulation and the gap between the studs. 

 

Finally plasterboard internally. You may need vapour retarder plasterboard/ foil backed to keep the vapour in check. 

 

To really add polish use blown cellulose  in the void. 

 

Pretty cheap and very easy to do in bits as it's all internal. Equally importantly, given your busy life at any point in the progress you can close the door and walk away as all the work is internal. 

 

As for the floor, Insulation board (as much as you can fit) and then a floating floor or 2 layers of staggered OSB. If you have the head height you could use a pumped screed with UFH. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

With the plywood layer being sealed, should the plasterboard be foil backed or plain? Just ordering materials, and realised not clarified that...

[Iceverge]

Use plain plasterboard. 

 

There's a risk with your external poly of trapping moisture in the wall otherwise.

 

Take care to seal all air gaps in the ply. Most moisture problems within walls/roofs are caused when drafts take damp air into the structure.