A big HELLO and a questions about insulation

[Otter]

Hello all, I recently found this community and I can't wait to get stuck in. As a novice to self building I feel like at this stage I will have more questions than answer for other people but I will keep active and offer advice where I can.

 

I have a farm with brick built stables, brick built out buildings, a barn and the main house. I am constantly working on the house when I am not at work and we hav recently passed planning to convert the stables and barn into two dwellings which we will do over time. 

 

My current project is to upgrade one of the brick storage buildings into a gym and would like advice on if I am making correct decisions. The building already has water and power, the roof has been replaced as it had no membrane and the battens had collapsed. I have taken up the floor which was made of a few hundred bricks laid on sand and replaced with mot and a concrete floor. The electrics are being upgraded to spec at the moment with a few extra sockets being added and the lights are being replaced with led.

 

My questions is around the insulation for the walls and ceiling. My plan for the walls is to use 47mm x 47mm battens, 50mm rockwool, vapor barrier and then 12.5mm plasterboard.

 

For the ceiling I am unsure at the moment, the rafters are 75mm deep so was thinking using 50mm of insulation block so leaving 25mm of breathing space above. Vapor barrier and then 12.5mm board. Unless I increase the depth of the rafters to add more insulation. The room is going to be used as a gym and wont be heated other than frost protection in winter.

 

Any thoughts or advice please, I am new to this so if this is way out from regs or anything else then please let me know.

 

Thanks

Rob

Edited March 13, 2023 by Otter

[SteamyTea]

Welcome.

Insulation is really very simple.

For any given material, it has a thermal conductivity, usually denoted as k or ⲗ.

This is amount of power, in watts, that can travel though the material for a given temperature gradient.

It is usually expressed as W.m^-1.K^-1.

Dense brick is around 1.3 W.m^-1.K^-1.

Mineral wool around 0.04  W.m^-1.K^-1.

 

From that you can calculate the R-Value which is just proportioning the k value for the thickness.

This gives the derived units of m².K.W^-1.

Just a case of dividing the thickness of the material by the k value.

So take a 100mm thick brick.

0.1 [m] / 1.3 [W.m^-1.K^-1] = 0.08 m².K.W^-1

Mineral wool at 50mm

0.05 [m] / 0.04 [ W.m^-1.K^-1] = 1.25 m².K.W^-1

All that is saying is for the same power transfer, you would can have an area 16 times greater for mineral wool than brick.

 

 

It is more usual to use U-Value as that is more intuitive.

The U-Value is 1 divided by the sum of the R-Values.  It has the derived units W.m^-2.K^-1.

 

U-Value [W.m^-2.K^-1] = 1 / R₀ + R₁

 

So

 

1 / 0.08 [m².K.W^-1] + 1.25 [m².K.W^-1] = 0.75 W.m^-2.K^-1

 

Doubling the thickness of the mineral wool insulation to 100mm.

 

1 / 0.08 [m².K.W^-1] + 2.5 [m².K.W^-1] = 0.39 W.m^-2.K^-1

 

Always worth making the insulation as thick as possible.

 

There is nothing to stop you having insulation thicker on some walls and thinner on others, it all contributes to the overall losses.

 

 

[Otter]

This is the room.

[SteamyTea]

1 minute ago, Otter said:

This is the room.

Easy to add 150mm of floor insulation onto that sand.

[Otter]

2 minutes ago, SteamyTea said:

Welcome.

Insulation is really very simple.

For any given material, it has a thermal conductivity, usually denoted as k or ⲗ.

This is amount of power, in watts, that can travel though the material for a given temperature gradient.

It is usually expressed as W.m^-1.K^-1.

Dense brick is around 1.3 W.m^-1.K^-1.

Mineral wool around 0.04  W.m^-1.K^-1.

 

From that you can calculate the R-Value which is just proportioning the k value for the thickness.

This gives the derived units of m².K.W^-1.

Just a case of dividing the thickness of the material by the k value.

So take a 100mm thick brick.

0.1 [m] / 1.3 [W.m^-1.K^-1] = 0.08 m².K.W^-1

Mineral wool at 50mm

0.05 [m] / 0.04 [ W.m^-1.K^-1] = 1.25 m².K.W^-1

All that is saying is for the same power transfer, you would can have an area 16 times greater for mineral wool than brick.

 

 

It is more usual to use U-Value as that is more intuitive.

The U-Value is 1 divided by the sum of the R-Values.  It has the derived units W.m^-2.K^-1.

 

U-Value [W.m^-2.K^-1] = 1 / R₀ + R₁

 

So

 

1 / 0.08 [m².K.W^-1] + 1.25 [m².K.W^-1] = 0.75 W.m^-2.K^-1

 

Doubling the thickness of the mineral wool insulation to 100mm.

 

1 / 0.08 [m².K.W^-1] + 2.5 [m².K.W^-1] = 0.39 W.m^-2.K^-1

 

Always worth making the insulation as thick as possible.

 

There is nothing to stop you having insulation thicker on some walls and thinner on others, it all contributes to the overall losses.

 

 

Thanks for the help. So with this I can get an R value but what about moisture and air flow between the insulation. I have read that air needs to get between the insulation and the roof tiles as that it vents. I am worried that if I get this wrong then I am creating a problem that can rot the structural wood. 

[Otter]

Damn, wish I had done that. The floor is down now. 

[Otter]

This is the room today with the delivery or plasterboard in it. 

[SteamyTea]

1 minute ago, Otter said:

Thanks for the help. So with this I can get an R value but what about moisture and air flow between the insulation. I have read that air needs to get between the insulation and the roof tiles as that it vents. I am worried that if I get this wrong then I am creating a problem that can rot the structural wood. 

The general rule, in the UK's climate, is to stop warmer, humid air, that is inside the building, migrating though the insulation onto the colder surfaces.

Depending on the types of insulation used, a vapour control layer is used on the inside, the warmer side, then the insulation, then an air gap for ventilation.

The problems start if the cold air, in the air gap, can bypass the insulation.  This makes the insulation a lot less effective as it, in effect, reduces the thickness.

There are insulations that are called 'Full Fill' that can cope with being damp for a short period of time, @joe90 used it on his walls I think.

There are roof system that do the same (warm roof).

 

[SteamyTea]

11 minutes ago, Otter said:

Damn, wish I had done that. The floor is down now. 

Do you have enough height to add insulation on top of the new screed?

Thermal losses though a floor are constant, all year round.

Edited March 13, 2023 by SteamyTea

[Iceverge]

Hi @Otter and welcome.

 

The first mm of insulation is the most important. Can you afford to loose any head height from the floor? 

 

If you could loose as little as 50mm

 you could put down:

 

25mm PIR.

11mm OSB floating on top.

11mm OSB offset from the first. 

 

It wouldn't be the last word in heat loss of course but it would make the room much more comfortable and much better than nothing. 

 

 

For the walls. There's many takes on internal insulation. Badly done it can be a recipe for disaster with condensation and mold behind the insulation and frost damage on the existing structure as the insulation will keep the wall cold. 

 

If you go down this route you must ensure that the wall doesn't take on excessive external moisture from wind driven rain leaky gutters etc and also that moist air cannot get to the wall in the first place. 

 

Most of all though it must be able to dry out again if it does get wet. 

 

 

 

 

[Otter]

3 minutes ago, SteamyTea said:

Do you have enough height to add insulation on top of the new screed?

Thermal losses though a floor are constant, all year round.

I will take a look at the floor tonight and see if I have the height. I don't really need to keep the room warm as it is a gym and wont have any heating anyway. Its more about damp control. Ive been in there recently and everything was damp and the electrics had cut out because the moisture was so bad. I think it was due to a sudden change in temperature outside. There are no doors at the moment, we took them off as they are just thin wooden stable style doors where the top and bottom open independently on a gate latch. 

 

I also need to keep the sound down as we want to play music in the gym and at the moment you can hear music outside really clearly. I am hoping that with insulations and proper doors we can reduce the noise outside. 

[Otter]

5 minutes ago, Iceverge said:

For the walls. There's many takes on internal insulation. Badly done it can be a recipe for disaster with condensation and mold behind the insulation and frost damage on the existing structure as the insulation will keep the wall cold. 

 

If you go down this route you must ensure that the wall doesn't take on excessive external moisture from wind driven rain leaky gutters etc and also that moist air cannot get to the wall in the first place. 

 

Most of all though it must be able to dry out again if it does get wet. 

 

 

 

 

This is my main concern. I don't want to do all this and have to rip it all out in 12 months

[SteamyTea]

7 minutes ago, Otter said:

I don't really need to keep the room warm as it is a gym and wont have any heating anyway. Its more about damp control.

The two go hand in hand as the dew point is related to temperature and pressure.

You may find that a simple and cheap to run Air to Air Heat Pump will give you all the climate control you need  They can warm and cool.

 

Reducing sound transmission is much harder.  It is a combination of absorption and decoupling.

There are decoupling bars (resilience bars) for plasterboard, worth fitting them.

 

It may be worth stopping for a few days and searching on here for suitable options.

But basically, what you want to do is insulate, reduce ventilation losses, then control those losses.

 

You could just give up exercise and spend all your free time on here with a beer and an ashtray.

Edited March 13, 2023 by SteamyTea

[Iceverge]

From a structural and safety point of view you always need to consider the effects of moisture on a building. 

 

Firstly external moisture. This is easier to visualise. 

 

1. Make sure the roof isn't leaking, valleys chimneys etc. 

2. Make sure that gutters are all working and taking water away from the building. 

3. Make sure no water is pooling by the external walls, correct sloping/french drains can solve this. 

4. Make sure that the water table isn't trying to push water up through the floor, again a french drain is a great and cheap way to solve this. 

 

 

Secondly internal generated moisture. Tougher to see as it's largely water vapour from breathing/cooking/showering drying clothes etc. It stays as suspended tiny moisture droplets in the air and forms into water droplets when it gets cold. Much like steam from a kettle condensing on a single glazed window. This is a real problem in almost all houses as it is hard to see and it's poorly understood. The consequences , mould, rot, damp and smells are widely known however. 

 

The air can suspend a certain amount of water vapour particles per m3 depending on temperature. At 4 deg it can hold 6.4g of water vapour per m3 of air. This is the maximum and is called 100% relative humidity (RH). You will see this as fog outside. However if you bring that m3 of air inside the house and heat it up to 20 deg it can hold much more moisture, 17.3g/m3. Given that it only has the 6.4g, that means it is nowhere near it's capacity to hold water. It's absolute humidity ( 6.4/m3) is the same but its RH has dropped to 37%.  This is why weirdly if you open the windows and doors briefly on a foggy day, let in 100%RH air, close the doors, allow the air to heat up it'll really aid the drying of the house as it can take on much more moisture. 

 

A similar thought experiment can be done in reverse.  Take your kitchen RH 70% and 20deg. That is 12.2g/m3 in absolute humidity. Unfortunately you have a poorly insulated window where the surface temperature is 12deg. The air that touches this gets cooled and it's RH climbs to 100% at 14deg. This is called the dew point as it is where dew begins to form. As the temperature of the air beside the window continues to drop the water vapour has nowhere to go and condenses out of the air making droplets on the window making an area for mould and damp. Not a massive problem if the window is in a breezy area of the house where it can dry when the RH drops again but a real issue where air movement is limited like behind furniture etc. 

 

 

The solutions for this are four fold. 

 

First ensure you have proper ventilation. It needs to be forced and continuous. Trickle vents and hole in the wall vents do nothing in still weather and too much in windy weather. This will take the internal air and replace it with external air that can help keep the house dry more. This was the a job of the fireplace in ye olde houses and mechanical ventilation in new ones. 

 

Secondly, build your house in such a way that no internal surface gets cold enough to collect condensation. This is typically a surface temperature of 16 deg for most houses. It can be easily achieved in a solid walled building by just running the heating a lot. A better way is to add a continuous layer of insulation. 

 

Thirdly, you need to do your utmost to prevent any moist internal air from getting into the structure of the house via cracks, holes and incomplete construction. 

 

Thirdly, keep the damp air out of the structure of the house where it could condense. This is done with a good airtightness layer. 

 

Fourthly you need to ensure that any moisture that gets into your structure can dry out as quickly and painlessly as possible again. Vapour open construction is best. 

 

 

 

 

I hope that wasn't too much theory. 

 

TLDR

 

Deal with bulk water from outside, it's easy to see and solve. 

 

Then deal with damp caused from inside via

 

1. Ventilation. 

2. Continuous insulation 

3. Airtightness

4. Vapour open construction.

 

 

 

 

 

 

 

 

 

 

 

 

[Iceverge]

 

With that in mind I would propose the following. 

 

FLOOR:

50mm PIR to the floor ( or as much as possible) 

2 x 11mm layers of OSB staggered, glued and screwed) 

 

 

WALLS:

 

75mm Cavity wall mineral wool slabs to external walls between 50mm X 50mm battens at 600 centres stood off the wall by 25mm spacers. 

Variable diffusion membrane to the inside like Siga Majrex 200 or Intello Plus. Taped very diligently to all penetrations, roof and floor and returned at least 300mm to all internal walls. It's important this has ZERO holes. All wires etc should be in the service cavity or taped completely airtight.  

20mm service cavity with battens ( or resilient bars) at 90 deg to wall battens for service cavity. 

12.5mm plasterboard

 

 

CEILING:

 75mm mineral wool batts placed across the rafters between battens to maintains 75mm ventilation above. 

20mm service cavity as above. 

2 x layers of 12.5mm plasterboard for noise. 

 

Obviously the suggested insulation values are only notional and more is always better. 

 

 

For ventilation a small MVHR unit like this would do the trick. As it's gym you probably wouldn't need any heating. 

 

 

[Otter]

8 minutes ago, Iceverge said:

 

With that in mind I would propose the following. 

 

FLOOR:

50mm PIR to the floor ( or as much as possible) 

2 x 11mm layers of OSB staggered, glued and screwed) 

 

 

WALLS:

 

75mm Cavity wall mineral wool slabs to external walls between 50mm X 50mm battens at 600 centres stood off the wall by 25mm spacers. 

Variable diffusion membrane to the inside like Siga Majrex 200 or Intello Plus. Taped very diligently to all penetrations, roof and floor and returned at least 300mm to all internal walls. It's important this has ZERO holes. All wires etc should be in the service cavity or taped completely airtight.  

20mm service cavity with battens ( or resilient bars) at 90 deg to wall battens for service cavity. 

12.5mm plasterboard

 

 

CEILING:

 75mm mineral wool batts placed across the rafters between battens to maintains 75mm ventilation above. 

20mm service cavity as above. 

2 x layers of 12.5mm plasterboard for noise. 

 

Obviously the suggested insulation values are only notional and more is always better. 

 

 

For ventilation a small MVHR unit like this would do the trick. As it's gym you probably wouldn't need any heating. 

 

 

This is amazing, thank you for this detailed response. I will read this and try and digest it all. 

[joe90]

8 hours ago, SteamyTea said:

There are insulations that are called 'Full Fill' that can cope with being damp for a short period of time, @joe90 used it on his walls I think.

Not only a short period, Indeed I did, 200mm rockwall batts, bba certificate for full fill and I can confirm that even with a soaked outer brick skin the water/damp did not migrate into the insulation ( I found this when I core drilled for the ASHP pipes after a very wet winter).

[SteamyTea]

7 minutes ago, joe90 said:

after a very wet winter

Had you put the silicone treatment on the walls by then, or was that after?

[joe90]

1 minute ago, SteamyTea said:

Had you put the silicone treatment on the walls by then, or was that after?

No I put it on the year after that again just in case. I only did the west facing wall as that caught the wet Atlantic driving rain (from Widemouth bay).

Edited March 13, 2023 by joe90

[SteamyTea]

8 minutes ago, joe90 said:

the wet Atlantic driving rain (from Widemouth bay)

Was camping there in August '79, when the Fastnet boat race was on.

My tent, along with several others, totally vanished.

Was a terrible night and next day.

[Iceverge]

25 minutes ago, joe90 said:

Not only a short period, Indeed I did, 200mm rockwall batts, bba certificate for full fill

 

Sounds like the most fire safe house on the planet. 

 

17 minutes ago, SteamyTea said:

Had you put the silicone treatment on the walls by then, or was that after?

 

Is that a brush on or spray?  Did you rate it? 

[joe90]

2 minutes ago, Iceverge said:

Is that a brush on or spray?  Did you rate it? 

Brush, dead easy (quicker than I thought). I rate it highly, https://www.kingfisheruk.com/supersilicon-item-26BA20#26ba5. Just one coat and water ran off it like glass 👍 I did it the summer after all the work so the wall was thoroughly dry when I did it.

[Iceverge]

‘The field tests show that a siloxane

impregnation, if properly applied, can repel rain

water to such an extent that a complete drying

of the masonry is possible…   It seems possible

that inappropriate impregnation can even

increase the moisture content and hence the

danger of frost damage… The quality of

workmanship and the preparation of the

façade, for example by repointing it, appear to

be of major importance.    If the quality

conditions are met, an impregnation can be

considered as an effective rain protection. ‘The field tests show that a siloxane
impregnation, if properly applied, can repel rain
water to such an extent that a complete drying
of the masonry is possible…   It seems possible
that inappropriate impregnation can even
increase the moisture content and hence the
danger of frost damage… The quality of
workmanship and the preparation of the
façade, for example by repointing it, appear to
be of major importance.    If the quality
conditions are met, an impregnation can be
considered as an effective rain protection.  
Small cracks up to 1mm do not affect the rain
protection if they are thoroughly impregnated
and if the walls if of sufficiently low air
permeability, e.g. by the application of a
plaster on the inside.’
Künzel & Kieszl (1996)

 

 

This suggests if done well it is a valuable addition. 

Edited March 13, 2023 by Iceverge