# Problems with current shop



## woodsworth (7 Mar 2010)

I guess this counts as a past mistake so hopefully some of you knowledgeable people can help me out with a solution. 

My shop has a coloured Tin roof. One of the problems with that is condensation building up on the inside of it and the dripping that produces. I thought it a good idea to insulate it so i glued insulation boards to it. Problem is because the tin is not flat condensation still builds up and now it drips though the seems in the insulation and down the beams it is attached to.

What do others do with this problem? I thought about dropping the insulation and giving it an air space but the same would happen. 

The other major problem is that the building was built with 8 inch blocks so i get a lot of damp coming through. What do people do in such a situation? I thought about knocking the whole thing down and building a workshop with straw bales but i need a place for all my equipment in the mean time and it''s not like i have a lot of money to throw at this problem.

Hopefully some of you have some creative answers that can help me out, thanks in advance.


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## OPJ (7 Mar 2010)

Sounds like some ventilation might help. If your workshop is long and narrow, two vents should help - one high, one low at alternate ends of the building. They will need X-amount of clear space surrounding them to get the best.


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## Sportique (7 Mar 2010)

Agreed Olly - you beat me to it  

Dave


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## woodsworth (7 Mar 2010)

The shop is 20 feet by 40 feet. Where did you have ventilation in mind? It isn't all that air tight. I wish it was then i could work in there when it is cold! But even with a heater i can't get it to many degrees warmer then outside temp.


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## matt (7 Mar 2010)

Between your insulation and the roof but, by the sound of things, it's all glued together. Moist air must be getting trapped between the two.


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## houtslager (7 Mar 2010)

many options to this, but are all dependent on the size of your wallet :lol: 

1. remove tin roof and repace with SIP panels
2. line i/s with "TYVEK" plastic sheeting with large overlaps and taped joints, then replace insulation under the tyvek.
3. put buckets in there to collect the water.

hth

k


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## trousers (7 Mar 2010)

Hi woodsworth

When you say coloured tin, do you mean the profiled and coated roof sheets?
In which case gluing insulation to the underside only has an effect on the flat parts, leaving the profiled parts uninsulated. Unless there is a lot of airflow through these profiled parts, thats where the moisture will condense.
As Houts has said, you probably need a vapour barrier like tyvek under the insulation. But I would strongly recommend that you have a ventilated airspace between the tyvek and the roof covering.
Or use the SIP panels for an all in one solution.
Either way, to do this properly you are looking at a re - roof if you want to end up with a warm space, especially if you can do something about insulating the walls as well.

Don't understand why your 8inch blocks are letting damp through. More info?


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## Lons (7 Mar 2010)

IMO as a builder you seem to have several issues:

If you are getting damp through the walls, you have moist air and this will condense on the underside of the cold roof as without adequate ventilation it has now where else to go. Are there eaves fillers in the profile where the roof meets the walls?

If the heater you use is not a dry heat (electric or oil filled rad) but is a calor heater or flame it will produce even more water vapour which = more condensation. (A calor heater produces gallons of water!)

You need to solve the wall problem:
If rising damp - inject a dpc
If penetrating moisture - paint the outside with Thomsons or similar or render it. or put up a breathable vapour barrier and fix 25mm slaters laths (you can fit 25mm polystyrene between if wished) and clad with plasterboard or ply.

Fit vents either end as high as possible to the roof to allow through ventilation and fit a breathable vapour barrier as others suggested.

Just one other point - check that no damp is entering through the floor.

Hope that gives food for thought

Bob


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## would not (7 Mar 2010)

How buildings cope with this problem that have steel linings and outer shells are to completely fill the void with insulation. 
My mate has one of these tin sheds and the inside is like being in a shower with the condensation problem. The only solution is to put a sufficient thermal barrier between the cold roof and warm moist air inside the shed, leaving a WELL ventilated void between the roof and insulation.

It's a bit like the flat roof situation, cold or warm roof. The ideal situation would be to have 4" kingspan etc right up against the tin roof. Problem is the tin roofs tend not to be flat so you'll always have some moist warm air against a cold roof hence the water. If you can't get rid of the gap then you need to improve the ventilation to it.

Or another answer is insulation on top of the roof and then another roof on top of that.


Edit - you can buy tin roofing panels with the kingspan type insulation molded to it hence completely getting rid of the void.


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## BradNaylor (8 Mar 2010)

I had a similar problem at my last workshop - a corrugated iron roof.

I solved it completely by having the underside coated with spray foam insulation. That stuff doesn't come cheap but it is bloody effective.

Still cheaper than a new roof, though!

Brad


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## woodsworth (8 Mar 2010)

Thanks everyone for your advice. Its funny Brad that was the original idea, to spray it. When i learned it would be over a £1000 i decided to look for other options. I will have to go with the spray insulation. 

Anyone know where the best deal is on that? I've found Xpandi foam has anyone used the kits before any tips would be appreciated. 

As for the walls. 


> Don't understand why your 8inch blocks are letting damp through. More info?


 To me it looks like the building was built with no foundation just a slab with walls on it. There looks to be a damp course between the slab and the blocks and that is about it. they used 8 inch blocks instead of using two four inch blocks with a gap in them. As i need to render the outside I am thinking that if i dig around the building and clean the walls and paint it with bitchimum paint and the thicker stuff where there is any honey combing, surround the building with a flexible drainage pipe covered with pea gravel and gardening fabric this will help with any damp getting into the base of the structure?

Then rendering it would stop any coming from the walls as people have suggested. I was also wondering if with these conditions if it is ok to build a stud wall inside with an air gap so i can insulate it or can i insulate the inside with the panels i will be pulling off the ceiling and board over them with plaster board?

I haven't ignored the suggestions provided just musing with the budget i have in hand, or will have over this year.



> When you say coloured tin, do you mean the profiled and coated roof sheets?



Yes that is exactly what they are.



> Edit - you can buy tin roofing panels with the kingspan type insulation molded to it hence completely getting rid of the void.



I've tried to find these, do you have any information, price on these?


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## llangatwgnedd (8 Mar 2010)

I used to have the same problem, I removed the corrugated sheets and laid plastic tarpaulin down as a sarking. 

With the walls, these where cladded with timber on the exterior. 

Problems solved.


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## trousers (8 Mar 2010)

Woodsworth

Reduce the ground level to 150mm below the dpc. This will stop any rising damp without having to do anything else.
If you have damp penetrating through an 8 inch block above the dpc your shop must be in a _very_ exposed location. If it is that severe, then rendering the outside will sort it (waterproofer in the undercoat). Masonary paint finish.
DO NOT apply bitumen to the outside of the walls. An moisture within the building will be trapped. Let the walls breathe.
Insulate walls internally. Free standing studwork or battens fixed to the walls, with rigid foam panels in between. Not sure a vapour barrier is necessary - the rigid foam boards have a foil face which is a good enough vb in this instance, esp so if you use osb as a cladding (p'board not very resistant to knocks).

Re the spray foam. Be aware this stuff gives off highly toxic fumes in a fire and drips molten bits everywhere. It is not easy to clad over to provide a fire resistant lining.
My preference would be for one of the insulated roof panels, as Would not suggested. Kingpan do one, but there are others.


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## Dibs-h (8 Mar 2010)

trousers":2z2epd2y said:


> Woodsworth
> 
> Re the spray foam. Be aware this stuff gives off highly toxic fumes in a fire and drips molten bits everywhere.



I thought the 2 part PU foams (sprayed) had some fire resistance?


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## trousers (8 Mar 2010)

Yes, some. A fire retardant is included in the formulation.

However, Building Regs state that *all* insulation materials should be installed behind a fire retardant barrier. The insulated roof panels have an internal lining for this reason, and to provide additional stiffness.

Woodsworth may or may not give a toss about the building regs anyway. He just wants a warm and dry workshop. You pays your money and takes your choice.


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## Dibs-h (8 Mar 2010)

trousers":1ofaitec said:


> Yes, some. A fire retardant is included in the formulation.
> 
> However, Building Regs state that *all* insulation materials should be installed behind a fire retardant barrier. The insulated roof panels have an internal lining for this reason, and to provide additional stiffness.
> 
> Woodsworth may or may not give a toss about the building regs anyway. He just wants a warm and dry workshop. You pays your money and takes your choice.



Ta!


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## woodsworth (8 Mar 2010)

> DO NOT apply bitumen to the outside of the walls.



I'm just curious why you wouldn't apply bitumen to concrete below grade? Wouldn't you want to stop moisture before it gets into the foundation?


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## trousers (8 Mar 2010)

Err...... I'm sure you said the walls were built on a concrete slab and that you wanted to bitumen the _walls_......? I didn't say anything about applying bitumen to concrete. 

[/quote]Wouldn't you want to stop moisture before it gets into the foundation?


> You said the walls didn't have foundations.
> 
> Normally a wall foundation is a (several) rows of bricks/blocks built on concrete in a trench around the perimeter of the building, and below a horizontal dpc. It doesn't matter if these blocks get wet as the dpc stops it rising into the walls above (provided the ground level outside is nominally 150mm below thw dpc).
> If your walls are built straight onto a concrete slab as you suspect and there is a dpc between the slab and the walls then the walls can only be damp if a) the ground outside is higher than the dpc or b) the damp is coming _through_ the wall.
> ...


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## woodsworth (9 Mar 2010)

I did a little jack hammering and trenching to clarify things, he did put a course of blocks under ground. So by your definition of a couple rows of brick being a foundation i guess it has one. 

The other thing is my partner wants to put a raised bed on one side of the shop and want to paint the wall up to that point with the bitumen to protect it. 

Where is the damp coming from? I haven't got a clue but I think through the walls and rising from the ground like everyone else who has damp problems. That's why i proposed the ideas i had to fix it, and why i asked why not paint bitumen on the outside of a wall. below grade, to clarify for you.

It still needs to be asked why you wouldn't put Bitumen on the outside when people also put a water proof rendering on the outside of buildings.

If i had time and money, i'd tear it down and save myself the grief. It is easier to start as a new build in my opinion then to fix something that someone has so thoughtlessly built. It's maddening!!! that such building get through. This one wasn't built without a permit, some hack built it so he could run a mechanics business from his home. Its just been there so long that they are accepting it.


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## trousers (9 Mar 2010)

> If i had time and money, i'd tear it down and save myself the grief.



:lol: :lol: 

Been there and done that :roll: 



> It still needs to be asked why you wouldn't put Bitumen on the outside when people also put a water proof rendering on the outside of buildings.



Bitumen (eg synthaprufe) type products are totally impervious to moisture. Any moisture within the building willbe unable to escape (except via draughts through doors/windows etc). It is good practice to let walls "breathe". The waterproofer admix in the rendering still allows this - it's a bit like a vapour barrier.



> my partner wants to put a raised bed on one side of the shop and want to paint the wall up to that point with the bitumen to protect it.



Not desirable really. Apart from the above, synthaprufe type products need to be protected (against uv and mechanical damage) so if used externally you would have to take measures to prevent this happening.
Usually, if part of a structure was below ground level (and hence dpc) there would be at least a cavity, and probably a self adhesive sheet type vertical dpc to prevent damp entering the building.



> Where is the damp coming from? I haven't got a clue



But how bad is it? Do you get a noticeable damp patch onte floor if you leave a piece of polythene weighted down a few days? Same with the walls? Are you sure it's not seasonal condensation (cycles of moist a nd dry air days).

I just think if you've covered all the bases I outlined in a previos post, then insulated, and got some heat (and ventilation) in there, a lot of your perceived damp may dissapear.


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## woodsworth (9 Mar 2010)

Well it's bad enough that anything put in close proximitry to the wall or on the floor it gets wet. I can't store wood against the wall or lean plywood up against the wall at all. I cut a kitchen and stacked it up against the wall so that when it was time to put them together i was a head of the game only to find out mould had decided to destroy almost every piece. 

I dug even further after work today and found that there is two courses of blocks below grade. They are quite saturated. I also jack hammered a bit of the floor out to see what was in place for damp course and while there is some poly there it is thin old and degraded. so not much use as a damp course or membrane. The damp course between the blocks is above the concrete slab on the inside and was not folded down to create a continuous membrane. 

So i think the damp is actually just coming straight in from the outside wall and into the slab.


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## trousers (9 Mar 2010)

Right.
The walls are on strip foundations and the slab has been cast afterwards with a lightweight poly membrane under it.
And there is a gap between floor level and the dpc in the walls.
So effectively damp will only enter in quantity via that gap, and especially if the outside ground level is too high.
The first thing is to get that ground level down, to at least below floor level. This will ensure that a lot less damp will be driven through the walls due to ground moisture retention.
I would then test to see how effective the floor membrane is by doing the test I mentioned before, but a little away from the walls. Even though the poly is thin it is probably still doing it's job (unless they damaged it when laying the concrete).
If the walls above the dpc are damp, due to rain penetration, then rendering or cladding the outside would be an answer. 
The damp coming through the wall at floor level can be overcome, but may require you to think about attending to the whole floor at the same time to ensure a 100% result.
At the end of the day you are going to have to decide how much money to throw at this thing.


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## woodsworth (10 Mar 2010)

> So effectively damp will only enter in quantity via that gap, and especially if the outside ground level is too high.



I won't be able to lower the grade the whole property slopes to the shop and as i said my partner wants a raised bed along that wall. This is why i introduced the idea of an exterior damp proofing to see what people thought.

However no one seems to think much of it at all. Is it people don't understand it or is there a problem with this form of damp proofing below grade?

In North America they bury houses 8 feet into the ground and waterproof the outsides of them in the same way i'm proposing. If there was some problem with it i think it would show up as flooded basements.


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## Dibs-h (10 Mar 2010)

woodsworth":3241yhwx said:


> In North America they bury houses 8 feet into the ground and waterproof the outsides of them in the same way i'm proposing. If there was some problem with it i think it would show up as flooded basements.



They do and they also wrap the bitumen with flat and dimpled membranes - lay ground drains (weeping tile) at the base of these walls. To just coat the walls and not protect them with membranes as Trousers stated they won't last for long.

If you read the data sheet on most of these products - they state that a membrane or protection board must be used. In your case a protection board would not be suitable.


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## woodsworth (10 Mar 2010)

What is the perforated drain pipe and gravel i'm back filling it with? I built houses in north America for approximately 20 years so i think i can say with confidence that what i'm suggesting is exactly how they build them there. The dimpled membrane is only extra insurance and is not necessary at all. I only ever seen that used on one house and that was because they built the foundation with insulated blocks filled with concrete. I understand if you are back filling with rubble that seems to be a norm here but i don't see that as suitable back fill and would be unthinkable in north america in fact you'd be told to dig it back up.

They use perferated pipe with good clean gravel and then it is either covered with building paper (a thin tar paper) or landscaping fabric and then back filled with a mixture of gravel and dirt.

I just want to make sure i'm not missing something here. i'll have the hole dug by the weekend and want to start painting it unless there is some very good reason that it shouldn't be done.


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## Dibs-h (10 Mar 2010)

woodsworth":1wf0ftsx said:


> What is the perforated drain pipe and gravel i'm back filling it with? I built houses in north America for approximately 20 years so i think i can say with confidence that what i'm suggesting is exactly how they build them there. The dimpled membrane is only extra insurance and is not necessary at all. I only ever seen that used on one house and that was because they built the foundation with insulated blocks filled with concrete. I understand if you are back filling with rubble that seems to be a norm here but i don't see that as suitable back fill and would be unthinkable in north america in fact you'd be told to dig it back up.
> 
> They use perferated pipe with good clean gravel and then it is either covered with building paper (a thin tar paper) or landscaping fabric and then back filled with a mixture of gravel and dirt.
> 
> I just want to make sure i'm not missing something here. i'll have the hole dug by the weekend and want to start painting it unless there is some very good reason that it shouldn't be done.



Land drain - Sorry comes from not reading posts fully.

I've seen the wraps and membranes on a fair few houses - almost all in cases where the original installation involved a bitumen 
based paint only.

I think the membrane should be applied - Synthaprufe certainly do cover it in their data sheets and I don't think it is because backfilling with rubble is the norm. Their product (as with most) has very little abrasion resistance - IIRC. Also you can't just paint the stuff on - some data sheets mention that joints in brickwork\block work must be "levelled off" with a Vandex type product first.

Be a shame to finish only to have moisture creep back in - when the cost of the "insurance" product as you called it, is marginal in the grand scheme of things.


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## trousers (10 Mar 2010)

Re Synthaprufe. It may be useful to read the data/application sheet.
They use phrases like "should be protected....." etc.

How are you going to prevent the damp that is entering via a pathway up through the foundation blockwork to above floor level, and below the dpc in wall which is higher than the floor inside? And this pathway is also compromising your floor membrane.
It seems to me that without adressing this problem, all the external work will be of little value.


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## woodsworth (10 Mar 2010)

hmmm ok below grade i was antisipating filling all gaps with a thicker tar product I only know it as pitch, it has to be trowelled on after it is clean and dry. Then paint on at least two maybe three coats of bitumen paint. This will go all the way up to 8 inches above grade. 

After this has set in a couple of days a shallow layer of gravel and then the perforated pipe will be rolled out and covered with about 6 inches to a foot of clean gravel. Then that will be covered with landscaping fabric. Oh and the trench is sloped so water does not sit. I am fortunate enough to have a sloping garden. they will be able to drain off unimpeded. 

I know this doesn't make it water proof it only makes it damp proof.

above grade will be re rendering. I haven't looked into all the products available but i assume that i will be mixing it with some form of acrylic or similar product to make it water resistant.

SYNTHAPRUFE looks more like it is used for tanking. I think that would be excessive in this situation. I am only looking to divert most of the water. Next year i'll be working on pulling the existing floor out of the building and digging it all out and suspend a wood floor.

I have given a lot of thought to ventilating the shop space as well. This was brought up several times. I think for that i will make a HVAC unit, they are designed to exchange the air every three hours and are about 97% efficient for heat loss. the idea is to pipe inlets close to the floor and outlets in the ceiling. This way i can get air flow without loosing heat in the winter.

The ceiling will be sprayed with polyurethane insulation. It will be protected by framing a ceiling but i want to get all the pipes in for the HRV unit and dust collection before i close it all off. Probably not till next year though, budget is already stretched.


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## trousers (10 Mar 2010)

Re the bitumen paint. Check the data sheets. They don't like tar/pitch substrates, or excessively damp.



> Next year i'll be working on pulling the existing floor out of the building and digging it all out and suspend a wood floor.



:shock: 

Best of luck with that one.


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## woodsworth (10 Mar 2010)

Well i wouldn't even think about it if it wasn't in a state. It was poured in about 6 pours non of which are remotely flat or level. It is hard to even sweep it.


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## chipchaser (21 Mar 2010)

Hi Woodsworth,

If you haven't found someone to spray insulate your workshop it may be worth trying this firm:

www.foam-insulation.co.uk

If your walls and floor are structurally sound you might consider dry lining the walls using studwork with insulation and, if there is enough headroom to spare, screeding the floor to level it over a new dpm. I would expect that to be much less work than breaking up the old concrete, carting it away and making a new suspended floor. The aim would be to create a dry insulated box within the existing shell. I would consider laying the screed over a layer of insulation but the energy saving is not as great as can be achieved by insulating the roof and walls so the pay back period is longer.

Graham

Edit just tried the link and found it suspended earlier today! Telephone number is 0800 019 6064


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## devonwoody (21 Mar 2010)

Seeing that you have a very large workshop, perhaps you could section off a part and build a smaller insulated workshop internally which might solve your main problem and let the problem area remain for activities that are not so demanding with regard to the condensation issue.


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## woodsworth (21 Mar 2010)

Thanks guys, i've looked into spraying it is very expensive! I found kits that i can do it for under a £1000 and it is my hope to have that done by winter. I am also planning on building a stud wall inside. Although i will loose a bit of space it won't be that much considering the benefits of a warm dry place to work in the winter. That along with getting a combination machine i'll have the room i need to do kitchens and bigger projects that I just don't seem to have the room to do right now with all the tools in there right now. 

Its money that is the issue really. Everything i make seems to be eaten up by maintaining current tools and buying tools to do the jobs i get. I haven't reached the break even point yet on this. Part of the problem is i'm doing things i really don't want to be doing but those seem to be where the money is right now. I'm renovating a cottage, i've gutted it, done the plumbing, plastered it built a fire place insulated the floor and am putting underfloor heating in it. Now i'm on installing a slate floor. It takes a lot of tools to be able to do all of these jobs and i'm constantly buying tools to keep up with the job.

I bought a belle 350 to cut the slate and the switch has gone on it and the blade is rubbish so now i'm buying a blade. I am also building some windows for a friend and have had to buy tools to do this. So much of my money goes back into this instead of gaining ground i'm supporting the business. I'm sure it is a tale most of you know already. 

The shop is the most important part for me as i see this as a place where i'll be able to build the things i want and sell them, but it will take time to get it into shape enough that i'll be able to do this. It is coming though. I've dug a moat around it and am damp proofing it, installing a washroom and a drainage system around the building so that any water that does get there will be diverted instead of sucked up by the block work. Then i'll be able to build the internal stud work and spray the ceiling. I can use all the insulation sheets on the ceiling for the walls, so those won't be a waste.

Time and money! if only those were more available.


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## devonwoody (21 Mar 2010)

And looking at your avatar, you need a pneumatic nail gun as well. :wink:


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## Thomasx (13 Dec 2010)

Hi Woodsworth

Did you go for the xpandi-fom diy-kit? How did it work out?
I am thinking of using it to isolate our house that we are renovating, and I am interested in some feedback on how the xpandi-foam worked, how it was to handle, to spray etc.

Thanks,

Thomas


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## Fromey (13 Dec 2010)

This sounds almost exactly like my shed when I 'inherited' it after buying our house. It looks like it was build by a bunch of boy scouts with no prior experience of building even with meccano.

Anyway, I fixed the leaking rusting tin roof by ripping it off and putting in new tanalised joists then weatherproof ply then two layers of felt. I then discovered the condensation malarkey last year. However, I've now insulated with that double-foil bubble plastic stuff glued on to the inside ply surface. Hopefully that should fix it.

For the walls, I painted the entire outside of the shed with about three coats of Santex paint. I made sure I trowelled lots of paint into all the cement-block texture. For the brick skirt, I painted it with a clear waterseal. It's done a great job of drying out the shed (it used to get about a centimetre of standing water on the floor!) except for a section of wall where the neighbour's soil is too high (next job).

A slight sideways question here;

If I have waterproofed the external of the shed with breathable Santex paint (allows the moisture inside to get out), would it be a wise/unwise next step to Santex paint the inside of the shed?


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