Shed Cladding

[elbekko]

Yikes. We had issues like that a few years ago with an exceptionally cold winter, lots of condensation on the ice cold walls leading to literal puddles under furniture. Now put 6cm of Recticel insulation plating against the walls.

[Anderzander]

Does that mean if I put an extra layer of board insulation in my loft it might create damp problems ? 

[Bowie69]

It depends where you put it.... There's quite a bit of science around insulation to prevent damp/condensation. 

[Ed Poore]

Sometimes the old ways are the best ways... 

House had a few damp issues when I bought it. Spent a summer with Mum's help hacking off the bodged concrete render on the outside. Couldn't actually find a firm (for a semi sensible price) who could rerender the house in lime so just settled on pointing it and a thin skim coat over the bodged in breeze block sections. Currently getting around to limewashing it. All the interior damp problems have gone now the stone can breathe. I think we've (or rather Tom our roofing neighbour) have finally found the last small leak in the roof.

Oh and so far 120 gallons of limewash has cost me £18 and the water. Damn sight cheaper than paint!

The roof spaces have mostly been insulated and we've replaced the last of the single pane windows with double glazed. Stopping the draughts has made a massive difference to the warmth in winter. It's not actually that bad to heat because 3ft thick stone walls work well at retaining the heat.

[bishbosh]

Loft spaces are either "warm" or "cold" depending on the ventilation design I belive (not an expert!). Get it wrong and you will have condensation issues.

[elbekko]

2 hours ago, Anderzander said:

Does that mean if I put an extra layer of board insulation in my loft it might create damp problems ? 

Probably the opposite. The issue is usually that when people insulate, they also get rid of all the draft. And it's the draft that takes away the moisture.

That and people putting in triple glaze windows without insulating the walls. Fog on windows = good, fog on walls = bad.

But extra insulation with good ventilation = less chance of damp.

[landroversforever]

1 hour ago, elbekko said:

But extra insulation in the right place with good ventilation = less chance of damp.

Edited! 

There’s a whole science behind warm/cold roofs around where a membrane and insulation sit. Get it wrong and stuff will rot if it’s hidden away. 

[Peaklander]

Warm or cold is the rafter position with respect to the insulation. If the insulation is underneath, then it's a cold roof. If it's in-between and/or on top, then it's a warm roof.

The roof ventilation, if it's required, is under the tiles / slates and above the (normally breathable) membrane and flows from fascia vents to the ridge (dry ridge). So right across the roof.

Habitable space ventilation is a whole different thing, from trickle vents to extract fans. This is needed to keep the relative humidity low. In a kitchen it would be easy to get towards 100% so extraction is needed.

6 hours ago, Anderzander said:

Does that mean if I put an extra layer of board insulation in my loft it might create damp problems ? 

This is what I have learnt whilst trying to specify my new roof:

I saw from the Kingspan condensation risk analysis for my roof that this can happen. What I managed to understand, is that for a given interior temperature and humidity, there's a dew-point temperature. At that point, water as vapour turns to water as liquid.

There's a temperature drop across your roof section, from warm inside, to cold outside. It drops across the plasterboard, rafters, insulation, across air gaps, tiles and battens. As it cools, the ability to hold water as vapour, reduces. So the humidity through the roof has to be reduced, by the action of the insulation, which prevents some of the vapour passing through. Think foil-backed plasterboard or foil covered rigid insulation with taped joints.

As the humidity reduces, so does the dew-point temperature. If the air (at a temperature and humidity) at any point in the fabric of the roof, were to reach the dew-point temperature (for that humidity), then interstitial condensation occurs at that position.

For example, to achieve U=0.16, Kingspan's calculation showed 75mm between my rafters and 60mm above. I have some 100mm available to go between (save money?). Their people ran the risk analysis again at 100mm and 60mm and it 'failed'. The 60mm would also need to be increased (to 80mm) - for the same U value of 0.16. I think that the 100mm would be 'too insulating', dropping the temperature too far at a point in the fabric where the relative humidity hasn't dropped enough.

 

Edited August 1 by Peaklander
Added last sentence

[Snagger]

On 8/1/2024 at 9:58 AM, elbekko said:

Best you can do is install a good ventilation system to prevent condensation and mold inside. Best overall improvement I've made to our house, it's a Vasco D275III with heat exchanger. Does require you to run a bit of piping, but a constant stream of filtered fresh air is great.

Mechanical Ventilation Heat Recovery (MVHR) is the term in the UK.  My father and brother have it on their new builds, mandated as they are high efficiency homes with very little leakage and would suffer terribly from condensation buildup without forced ventilation.  Older housing stock relied on drafts through the window and door frames, and once double glazing became common, the trickle vents at the tops of the window frames.  But those drafts lose heat, where MVHR retains the heat by using the exhaust air to warm the fresh incoming air.  A double-glazed house with the trickle vents left closed will become damp and can get condensation on the windows or the interior surface of outer walls, or both, especially where plumbing penetrates the walls or where insulation is poor.

Damp coming through from the wall cavities is a sign of problems in the roof.  The tops of the cavities are supposed to be well covered but ventilated, but often aren't and any leaks or pooling in the roof space can get into the cavity from the top.  The problem might be a failed membrane under the tiling, the membrane finishing too short of the eaves or soffits, insufficient runoff gradient, blockages by moss and dirt or loft insulation blocking cavity ventilation or wicking water from the soffits to the cavity.  All seem common issues, from what I have read and watched.  Skill Builder has useful videos on it on youtube.