Drylining window reveal

TiNcAn

I am looking for advice on how to do construct the drylining surrounding a window reveal. It is an old red brick house with solid walls. The dry lining system I plan to use is as follows:

- Lime plaster basecoat
- 80mm wood fibre insulation
- Vapour check membrane
- Wooden battens to provide service cavity
- Plasterboard

The tricky part is dealing with the windows. I have attached a couple of pictures to show what it actually looks like and the different options that I am considering. Because of the peculiar window reveal it is difficult to find an easy approach. So advice is appreciated.

TopTec

I've an old stone and concrete block cottage which I internally insulated. When it came to the reveals I dot and dabbed the 12mm board onto the walls. Never had a problem with damp or moisture ingress.


TT

TiNcAn

What sort of insulation type did you use? And how did you manage to get an airtight seal around the window?
As you can see in the picture, I don't know if a dot and dab board around the window would work because of the awkward shape.

listermint

Contiga SL tape for airtightness and the dot and dab would work fine.

TiNcAn

Thats exactly what I was thinking for the air tightness tape. The Congia SL tape can be stuck to masonry and plastered over so it is a good match for this job.

But I am still unsure about which of the 3 options to go with for above as shown. Or is there an easier approach all toghether? Essentially I want to seal the window tight while still keeping it insulated and with plasterboard around the reveals.

TopTec

I used 12.5 mm insulated plasterboard... any more and the board would of intruded too far over the window frames, taped and plastered the seal is airtight.... never a draught.

TT

Wartburg

Self-adhesive window tapes like Contega SL or Fentrim are in the most cases not the best option for standard reveals in Ireland. The surface is too rough and needs to get pretreated as stated in the installation manuals of the tape manufacturers. In the best case by using a primer, in the worst case scratch coat and primer. The better option is a window tape, which gets bonded to the block/ brick by using additional adhesive. Depending on the structure of your substrate, you can apply a thinner or thicker bead and your window tape is onehundred percent sealed.
As a side note: if you install the vapour control membrane above the wood fibre board, you destroy the benefit of the wood fibre insulation. She can level the humidity in your rooms by absorbing moisture. The VCL has to be installed under the wood fibre insulation layer. You should think about a paintable or sprayable solution.

TiNcAn

That is interesting stuff Wartburg. I was also intending to use the glue adhesive to seal create a good bond with the masonry and will nonentheless put on a scarth coat since the entire wall will be replastered to take the insulation

I have read much about this and I know types of insulation and membranes for solid masonry walls are a big point of discussion. In this particular scenario my understanding the vapour control membrane will reduce the amount of moisture travelling into the walls from inside when there is high humidity in the walls. The clever part is that it still allows moisture to move from the wall inside during drier months allowing the wall to dry out.
I received a short report where this was checked in a DEWI calculation but I wouldn't bet the house on it but also try to find out what others experience is in this area.

In any case, it is not really possible to put the vapour control membrane on the 'cold' side of the insulation because boards must be applied to the wall with wet plaster. This is to avoid any air gaps for condensation to arise.

TiNcAn

TopTec wrote: »

I used 12.5 mm insulated plasterboard... any more and the board would of intruded too far over the window frames, taped and plastered the seal is airtight.... never a draught.

TT

I may consider taking a shortcut and using this approach for the window reveals. It is certainly a lot easier and simplier and would yield similar thermal results. It does run a higher risk of mositure buildup and what that brings (i.e. mould) but it hopefully would not be the case. I'll need to think a bit more about this before a decide on which option to take.

Wartburg

TiNcAn wrote: »

In any case, it is not really possible to put the vapour control membrane on the 'cold' side of the insulation because boards must be applied to the wall with wet plaster. This is to avoid any air gaps for condensation to arise.

And that´s exactly the point why you should consider a sprayable or paintable VCL, if you really require it. Alternatively you can use clay plaster underneath the wood fibre board insulation because this type of plaster will balance the moisture. A water repellant coating on the external side of your brick wall needs to be considered as well.

TiNcAn

I definitely agree with using a water repellant on the external side of the brick wall and have already removed the pebbledash a purchased some siloxin based sealant for the job. 

I have considered clay plaster but will stick with lime since there is more experience working it and I already have already gotten the plastering materials for the other internal walls. 

The VLC works by having a high Sd value when the humidity is high and visa versa. 
If the VCL is placed on the warm side this will slow but not stop the transfer of water to and from the insulation & wall during high humidity and allow drying out towards inside of the room during warmer periods. 
If the VCL is placed on the cold side this makes it makes it more difficult for the mositure absorbed by the wood insulation to transfer to the external masonry walls when the humidity is high in the wall. I think it all cases you want to have as low as Sd value between the insulation and the wall to allow it to dry out as best as possible. So would it not be better to place the VCL on the warm side since most of the moisture will come from inside the room?

dathi

option four would be to double up the thickness of insulation from 80mm to 160mm in the reveal and add larger batten in corner to make up any discrepancy in thickness

TiNcAn

That would be a good option but as I pointed out in options 2 & 3, I don't have anywhere to fix a batten close to the window frame which I would need to use to secure the plasterboard. Any suggestions on how to get around this (glue the batten to the window frame?)

listermint

Wartburg wrote: »

Self-adhesive window tapes like Contega SL or Fentrim are in the most cases not the best option for standard reveals in Ireland. The surface is too rough and needs to get pretreated as stated in the installation manuals of the tape manufacturers. In the best case by using a primer, in the worst case scratch coat and primer. The better option is a window tape, which gets bonded to the block/ brick by using additional adhesive. Depending on the structure of your substrate, you can apply a thinner or thicker bead and your window tape is onehundred percent sealed.
As a side note: if you install the vapour control membrane above the wood fibre board, you destroy the benefit of the wood fibre insulation. She can level the humidity in your rooms by absorbing moisture. The VCL has to be installed under the wood fibre insulation layer. You should think about a paintable or sprayable solution.

Contega is designed for this application and when used in conjunction with Orcon F on the masonry side is perfect for this application.


Why because I've used it many times. Read the literature

builditright

Hi
Another excellent solution would be the Isocell Isowindow products, I have used this many times, they have several options depending on whether you want to stick the window tape to the wall with adhesive in a tube or use a full adhesive tape similar to Siga, they have one similar that works well for rough dusty reveals as in your picture , all work with the detail you have and bond extremely well to clean or prepared concrete, they also have an excellent spray primer and a brush on one similar to Siga , in my experience the spray on is the best . In any case for your detail in the picture you will need to prime the reveal no matter what product you use. Some say that the Siga products does not need priming this will not be true in your case, any tape that I have ever used on concrete achieves the best results with priming unless the concrete is totally dust free I would strongly recommend priming . Looking at your pictures best approach would be to dust down, prime the reveal 2 times , first one to seal into the porous surface and bond any remaining dust, second coat to give a better overall adhesion, allow the primer to dry between coats and before applications of tapes (it will never dry completely but when it is tacky but not wet you can go again) , around 20 minutes between coats depending on the day that is it . Wipe any dust/ dew off window frame , apply the tapes with firm pressure using a roller , you may find using a rag will help to apply pressure on any uneven surfaces, allow the tapes to cure for 24 hours , they take that long to get full bond. You can plaster over any of the options above, or you can just put a dab ad dot liner over them without any problems. If you want further information you can PM me.

BryanF

Wartburg wrote: »

if you install the vapour control membrane above the wood fibre board, you destroy the benefit of the wood fibre insulation. She can level the humidity in your rooms by absorbing moisture. The VCL has to be installed under the wood fibre insulation layer. You should think about a paintable or sprayable solution.

Vapour barrier warm side of insulation

As a side note: What window tape do you sell?

Wartburg

listermint wrote: »

Contega is designed for this application and when used in conjunction with Orcon F on the masonry side is perfect for this application.


Why because I've used it many times. Read the literature

I do not disagree. Every window tape with an additional adhesive is suitable for the application. Doesn´t matter what kind of imprint the tape has.

TiNcAn

I plan to use thoroughly clean the reveal surfaces then use the Orcon F on the masonry. I presume this would be sufficient to get good adhesion between the tape and the masonry. 

But I am still unsure how to build up the reveals. Since I don't have a way to fix a batten adjacent to the window frame this rules out option 2 & 3. Which leaves me with option 1 where I will screw a batten through the insulation into the brick, and then use this batten to secure the plasterboard.

One other option as suggested would be to use dot & dab with 20mm insulated plasterboard. Or similarly 20mm wood insulation with screwed plasterboard as shown in the image below. 

Which approach seems like the best way forward here?

builditright

Hi , just having another read of the above posts and I see the following suggestion by Wartburg :

"The VCL has to be installed under the wood fibre insulation layer. You should think about a paintable or sprayable solution."

I am sorry but THIS MAY NOT BE GOOD ADVICE.

The Airtight vapour control layer should always go to the warm side of the insulation, and in any case only 30 per cent of the insulation should ever be on the warm side of the VCL , in your case it looks like the wood fiber is the only insulation in the wall makeup and you need to prevent a dew point from occurring at the face of the cold wall, if you put the membrane to the back of the wood fibre you run a much higher risk of condensation forming potentially both sides of the membrane as the hot humid air the wood fiber is absorbing from the room will hit the cold wall/membrane and once you have a 7 degree differential moisture will form, so be very careful about where you place the vcl , in your make up the internal side of the wood fiber is the safest place and in my opinion the only place. Also you will need a variable membrane similar to Isocell Airstop Diva Forte or Intello.

If you want to go through your potential options in more detail I am happy to help if you pm me.

builditright

Build a full height frame in front of the window opening, in the same plane as the insulation, side rail to the left and right and then top and bottom rail across the top and bottom of the window, butted up to the insulation layer, mechanically secure your plasterboard back to the frame, and adhere the plaster board back to the wood fibre at the window frame side using Airstop joint paste, don’t know how to post an image? You have a WEAK POINT in both of your proposed solutions, you need AT LEAST the full 80mm of insulation to face of the block work ALL THE WAY AROUND YOUR REVEAL , the areas that only have 20 mm to face of the wall and return is not a good idea, you will have problems in this area as heat will find the weakest link within the insulation layer and pass through this area at a higher rate than the rest so it will be like water going through a hose it will go out through this location rapidly and cause potential condensation. If you Pm me I can go through the correct approach with you. I am new to this message board so I don’t know how to PM. but the right solution is actually very simple. And yes, I am a professional in insulation, airtight structures and low energy and passive buildings and we do sell products, but we are here to help, for us the most important thing is that it’s done right, I don’t care what product you use, you’re only going to do it once, so you might as well do it right, well hopefully anyway.

Wartburg

builditright wrote: »

Hi , just having another read of the above posts and I see the following suggestion by Wartburg :

"The VCL has to be installed under the wood fibre insulation layer. You should think about a paintable or sprayable solution."

I am sorry but THIS MAY NOT BE GOOD ADVICE.

The Airtight vapour control layer should always go to the warm side of the insulation, and in any case only 30 per cent of the insulation should ever be on the warm side of the VCL , in your case it looks like the wood fiber is the only insulation in the wall makeup and you need to prevent a dew point from occurring at the face of the cold wall, if you put the membrane to the back of the wood fibre you run a much higher risk of condensation forming potentially both sides of the membrane as the hot humid air the wood fiber is absorbing from the room will hit the cold wall/membrane and once you have a 7 degree differential moisture will form, so be very careful about where you place the vcl , in your make up the internal side of the wood fiber is the safest place and in my opinion the only place. Also you will need a variable membrane similar to Isocell Airstop Diva Forte or Intello.

If you want to go through your potential options in more detail I am happy to help if you pm me.

I did a quick simulation myself and have to agree that the VCL under the wood fibre insulation is not suitable for your case. My main intention was, that the vcl on top of the wood fibre eliminates the sorption benefit almost completely. The only benefit, you still have is the better heat storage capacity in comparison to standard mineral wool.
I know for sure myself that the VCL has to go to the warm side of the building and that you can use only x-amount of insulation above.

The tricky point with your proposed structure is, that my simulation calculated a noticable condensate by having 20°C / 60% rel. humidity internally and 0°C / 85% rel. humidity externally. A humidity variable VCL, namely I...... Plus was already included in the simulation.

Wartburg

BryanF wrote: »

As a side note: What window tape do you sell?

Have no need to do any advertisement here.

builditright

Hi Wartburg,
Thank you for the info.
I have not done a calculation as of yet, but , if you are seeing condensation with the proposed make up then then it might be that thicker insulation may be required, or a vented cavity to the rear of the insulation . how much condensate are you seeing and what is the drying out period?

Wartburg wrote: »

I did a quick simulation myself and have to agree that the VCL under the wood fibre insulation is not suitable for your case. My main intention was, that the vcl on top of the wood fibre eliminates the sorption benefit almost completely. The only benefit, you still have is the better heat storage capacity in comparison to standard mineral wool.
I know for sure myself that the VCL has to go to the warm side of the building and that you can use only x-amount of insulation above.

The tricky point with your proposed structure is, that my simulation calculated a noticable condensate by having 20°C / 60% rel. humidity internally and 0°C / 85% rel. humidity externally. A humidity variable VCL, namely I...... Plus was already included in the simulation.

Wartburg

builditright wrote: »

Hi Wartburg,
Thank you for the info.
I have not done a calculation as of yet, but , if you are seeing condensation with the proposed make up then then it might be that thicker insulation may be required, or a vented cavity to the rear of the insulation . how much condensate are you seeing and what is the drying out period?

200 gramm/m² and a drying time of close to 70 days (69 as far as I remember). I used the rigid wood fibre boards for internal insulation, made by G...X Because I do not know the exact original structure, please take the calculation as a rough indicator. I used 2 100mm solid brick walls with a 50mm cavity and a 200mm solid brick wall as alternative. The difference between both structures was around 10 gramm/m².
A nice 450mm solid brick wall, as I often had it in the Gründerzeit style buildings in Germany, would make it much easier. I remember that we had to use humidifiers sometimes, to bring the relative humidity above 40% in these buildings.

TiNcAn

Wartburg wrote: »

builditright wrote: »

Hi Wartburg,
Thank you for the info.
I have not done a calculation as of yet, but , if you are seeing condensation with the proposed make up then then it might be that thicker insulation may be required, or a vented cavity to the rear of the insulation . how much condensate are you seeing and what is the drying out period?

200 gramm/m² and a drying time of close to 70 days (69 as far as I remember). I used the rigid wood fibre boards for internal insulation, made by G...X Because I do not know the exact original structure, please take the calculation as a rough indicator. I used 2 100mm solid brick walls with a 50mm cavity and a 200mm solid brick wall as alternative. The difference between both structures was around 10 gramm/m².
A nice 450mm solid brick wall, as I often had it in the Gründerzeit style buildings in Germany, would make it much easier. I remember that we had to use humidifiers sometimes, to bring the relative humidity above 40% in these buildings.

You are actually very close to the products which I was planning to use. The wall itself is a solid masonry with clay brick around 220mm thick.

Do you think the amount of condensate buildup is of a concern? A vented cavity to the rear would not be my preferred mitigation since it ends up taking yet more space off the internal room. Does it help to remove the VCL to retain the absorption benefits of the wood insulation?

Lumen

Don't understand the logic of a VCL in a red brick and Gutex wall. Surely you want the wall to be vapour permeable to allow drying out in either direction depending on weather conditions?

TiNcAn

Lumen wrote: »

Don't understand the logic of a VCL in a red brick and Gutex wall. Surely you want the wall to be vapour permeable to allow drying out in either direction depending on weather conditions?

That is exactly what it does. In warmer weather it makes it easier for the wall to dry out towards the inside. Otherwise it drys out towards the outside.

Lumen

TiNcAn wrote: »

That is exactly what it does. In warmer weather it makes it easier for the wall to dry out towards the inside. Otherwise it drys out towards the outside.

Thanks. Found this explanation.

"The latest type of VCL membrane is the 'intelligent' membrane. This is a very useful product that remains very vapour tight during the winter months where it is important to try and prevent moisture from entering your structure from the interior. As temperature and humidity in the walls rises the pores in the membrane open and allow moisture to migrate towards the interior of the building. This gives the best of both worlds and ensures your structures remain as dry as it is possible to be."

builditright

Hi I have done a quick calculation on this for you,

After running the calculation, the drying out time as Wartburg has already pointed out even with a variable/smart membrane could be excessive particularly if you have a higher relative humidity within the home than normal, or perhaps an extremely cold winter outside, the amount of condensate at 60 per cent internal humidity is high and the drying out time may be beyond what is normally acceptable, at 45 per cent still resulting in condensation that requires 46 days to dry out but that is getting better . 40 per cent humidity does bring the drying out time down to 35 days which is just crossing over to being acceptable. I assume you don’t have heat recovery within the home? This would help control internal humidity if you did. Ideally your humidity in the home should be around 45 % in any case, make sure you don’t create excessive moisture by drying cloths in the house, and make sure bathrooms have more than adequate extraction for humidity from the showers etc.

Software can only tell us so much, a bit of common sense is also needed, the condition of the brick and the mortar joints will also have an impact on the drying out time, obviously if there are any cracks even hairline this will aid with potential drying out towards the outside of the structure, however likewise if they are cracked outside this could bring in more moisture from the outside. Its important that you have a good sealed exterior finish. (You also need to avoid paints that are not vapour open inside and outside)

Situations like yours may not always have a perfect solution . You have a complicated makeup at least from a physics / condensate perspective. The wood fibre will help in that it will disperse the moisture through it and reduce pooling, as well as help to transport it back to the inside where it can dry back out to the inside of the building during the drying out months, but for this to work the wood fibre need to be firmly pressed up to the face of the block work, a tight fit, no gaps if possible. If your blockwork is extremely rough or uneven a coat of smooth sand and cement ( correction - use a Lime Coat has better diffusion properties) to its face to create a smooth even surface for the wood fibre to be applied to may be a good idea. With your make up you will get condensate no matter what you do, and if you do put in a void to the back of the wood fibre then it needs to be well vented, or you could end up with a pool of water at the base of the floor.

I think if you use a variable membrane such as Airstop Diva Forte or Intelo (Not using a variable membrane will make the condensation a lot worse, not recomended), coupled with the wood fibre insulation fitted tight to the wall surface, this will give you the best possible solution for the detail you have, make sure you don’t use plasterboard with a foil back and avoid vapour tight paints and certain wall papers. Also don’t forget to eliminate areas of the insulation that are less than the 80mm around your reveals. Build a frame around your window in the same plane as your insulation to finish off the plasterboard reveal.

I hope that all makes sense.

TiNcAn

builditright wrote: »

Hi I have done a quick calculation on this for you,

After running the calculation,  the drying out time  as Wartburg has already pointed out  even with a variable/smart membrane could be excessive particularly if you have a higher relative humidity within the home than normal, or perhaps an extremely cold winter outside, the amount of condensate at 60 per cent internal humidity  is  high and the drying out time may be beyond what is normally acceptable,  at  45 per cent still  resulting in condensation that requires 46 days to dry out but that is  getting better . 40 per cent humidity does bring the drying out time down to 35 days which is just crossing over to being acceptable. I assume you don’t have heat recovery within the home? This would help control internal humidity if you did. Ideally your humidity in the home should be around 45 % in any case, make sure you don’t create excessive moisture by drying cloths in the house, and make sure bathrooms have more than adequate extraction for humidity from the showers etc.

Software can only tell us so much, a bit of common sense is also needed, the condition of the brick and the mortar joints will also have an impact on the drying out time, obviously if there are any cracks even hairline this will aid with potential drying out towards the outside of the structure, however likewise if they are cracked outside this could bring in more moisture from the outside. Its important that you have a good sealed exterior finish.  (You also need to avoid paints that are not vapour open inside and outside)

Situations like yours  may not always have  a perfect solution .  You have a complicated makeup at least from a physics  / condensate perspective.  The wood fibre will help in that it will disperse the moisture through it and hopefully reduce pooling, as well as help to transport it back to the inside where it can dry back out to the inside of the building during the drying out months, but for this to work the wood fibre need to be firmly pressed up to the face of the block work, a tight fit, no gaps if possible.  If your blockwork is extremely rough or uneven a coat of smooth sand and cement to its face to create a smooth even surface for the wood fibre to be applied to may be a good idea. With your make up you will get condensate no matter what you do, and if you do put in a void to the back of the wood fibre then it needs to be well vented, or you could end up with a pool of water at the base of the floor.

I think if you use a variable membrane such as Airstop Diva Forte or Intelo , coupled with the wood fibre insulation fitted tight to the wall surface, this will give you the best possible solution for the detail you have, make sure you don’t use plasterboard with a foil back and avoid vapour tight paints and certain wall papers.  Also don’t forget to eliminate areas of the insulation that are less than the  80mm around your reveals.  Build a frame around your window in the same plane as your insulation to finish off the plasterboard reveal.

I hope that all makes sense.

Wow! I must say that this is very in depth analysis and really makes a lot of sense when broken down like that. As you said, simulations help to understand what is going on but it will ultimately come down to common sense and experience.

In this sense there are a lot of things to consider to make sure that the presence of moisture is reduced so far as possible. Thankfully the bathroom is at the back of the house in an extension that has forced ventilation,  washing machine and dryer are out the back. There is an plain open vent in the walls that I plan to upgrade these to a more modern version with baffles, but don't think I will go so far as MVHR. For the outside wall I have also begun to repoint the wall and will apply some Silane/Siloxane coat to act as a water replant.

For the interior walls I have removed all old lime and cement plaster and am in the process of cleaning the brick surface of the remaining residue which is a really messy job. Then a scud coat followed by a scratch coat of  lime plaster. And then finally apply a final cost of limeplaster to the wall together with the wood board. I also decided to go with the St. Astier NHL3.5 lime plaster from a local supplier for all these coats instead of the branded products lime like 'Solo universal coat' etc. but don't expect this to be an issue. Your suggestion the previous post for using full length frame with Airstop is a good suggestion since it allows to fit in 80mm of insulation around the reveal.

It is quite suprising that even going down the road using products that are specifically designed for this purpose and making sure to avoid any air gaps and so on, that there is still a possiblity for mositure problems to occur. Espeically when you hear of some many people who just whack up dot & dab insualted plasterboard and the like and never report a problem. I often question myself whether this is more academic and reality allows for a much greater leeway than expected. Especially when you consider the large housing stock in Ireland which are of solid masonry construction.  So it really is more effort to go down this road and don't think most builders would be appreciate the care needed when working with these older homes, nor homeowners willing to accept the additional cost compared to traditional techniques.

Wartburg

I simulated various options with your proposed wood fibre insulation but they all ended with more or less the same condensate , as I stated before. You need to have a VCL, otherwise your wood fibre board will be drown.
You might should use a hygrometer, to check and trace your existing relative humidity. I´d say the 45% rel. humidity, as builditright suggested for an ideal case, are hard to reach with your existing structure.
It´s probably safer to stay with the limecoat for rendering to the bricks. In the worst case, the bricks may not harmonize with the suggested cement and you open another battlefield.