Cold bridging?

David_Aldred

Hi Dampdaveski,
The PIV units are very good and in much of the work I do for Housing Associations they are recommended to be fitted as part of the package in addressing excessive humidty issues along with humidistat controlled extractor fans and other support measures.

For those not familiar with PIV units they are a fan with a filter on that takes air usually from a loft void and blows it quietly into the property often on the landing through a grill in the ceiling but they can be fitted elsewhere if this is not possible / appropriate.

This action of blowing air into the dwelling causes a positive presure in the property compared with outside and as everything wants to be in equilibrium this encourages the moisture laden air within the property to permeate outwards through the fabric of the building / windows / doors / vents etc. Thereby in principle this process should help to lower the relative humidity within the property and consequentially the risk of condensation / mould grwoth.

They are not the be all and end all but they are a good support measure if you can afford to buy one / have one fitted (though they are not particularly cheap depending upon the route you buy one) or even make one (I have known people do the latter as they are really only a glorified fan with a filter on).

Some of the more costly units can also incorporate heat recovery which is always nice to have as an added bonus. Fitted correctly by an NICEIC electrician they are quiet and should be as cheap to run as a fridge. Tenants have sometimes complained when the fan goes noisy or they feel they are causing a cold draught and have gone up into the loft void and turned them off followed by a complaint the mould is making them poorly so that can sometimes be a bit of a job trying to explain the benefits of having the unit switched on.

Kindest regards, David Aldred independent damp and timber surveyor

David_Aldred

Hi Princessamy - didn't get the private message but if you are not so far I'll come out for free because I am nice that way (laughing) and have a look in the cavity with a photographic endoscope / a chat from somebody who is not going to flog you anything. All the best, David Aldred

2Sheds

David_Aldred wrote: »

.............or they feel they are causing a cold draught and have gone up into the loft void and turned them off followed by a complaint the mould is making them poorly so that can sometimes be a bit of a job trying to explain the benefits of having the unit switched on.

Kindest regards, David Aldred of Aldred Ltd Independent dampness and timber surveyor

We've fitted one in our 3 storey town house, which has the lounge on the middle floor and an open staircase to the top floor. A bit nippy in the lounge with the draught from the PIV unit. Last night the air coming into the house from the loft via the fan was only 12 degrees.

rhubarbcottage

Very interesting reading.

Regarding the wall ties, a neighbor had that done with a bolt that had expandable ends. These went through the middle of a brick. A spanner then expanded one end in the inner brick, then the end in the outer brick to hold the walls together. Would that be okay for an insulated wall? I assume there'd be no debris other than a little brick dust?

Again, very interesting post and of good use to us for the future since our walls are insulated, it's an old property and wall ties will be an issue at some point.

David_Aldred

Hi rhubarbcottage,
The design of the replacement tie is dependent on the substrate into which it is being fixed and the type described by you is a standard double mechanical fix - that is it fixes mechanically both ends as opposed to be being fixed by a resin at one end or both. Under nornal circumstances with good substrate that type of tie you describe is fine though somebody other than the contractor should ideally have pull tested sample ones to check adequate fix.

It is important that the replacement ties are angled slightly upwards from the outer leaf of brickwork to the inner leaf so that this resists any risk of penetrating dampness running down the tie and into the property. The tie should have a little rubber gromet on it half way along to help resist this issue as the gromet acts as a drip point. If the tie slopes down towards the inner leaf the rubber gromet may not be enugh to stop such moisture running down and into the inner leaf especially when surrounded by insulation.

You might think there would be nothing more than a little brick dust associated with such work but this is often not the case when the poor guy putting them in all day is stood on ladders holding on in desperation with one hand and pushing like mad a heavy industrial hammer drill with a foot long masonry drill attached to it with the other and that drill is shaking and snatching all over the place. The mechanical hammering of the drill is just that - a hammer action and the substrate brickwork is often poor. In any case the brick is considerably weaker in tension than it is in compression. As the drilling gets towards the rear face of the outer leaf of brickwork it is not uncommon at all for it to suddenly break away as a chunk of brick in various sizes. I have photographs of this. As indicated in the post above this brick debris then sits upon the insulation if the cavity wall insulation has been put in first.

The contractor is not going to open the wall up to get the piece of brickwork out - he just goes oops and carries on each and every time it happens - hoping he doesn't get white finger and deafness with all that drilling for a living and praying he doesn't fall from the ladders.

These are comments from many years experience of working with people who did this for a living and occasionally helping putting many cavity wall ties into walls whether they had insulation in the cavity or not and also looking into cavities of walls for a living whether they have been re-tied or not so the comments are factual not a hypothesis - what a game.

Hope this helps,

Kindest regards, David Aldred of Aldred Ltd Independent dampness and timber surveyor

joyciebird

David_Aldred wrote: »

Hi Princessamy - didn't get the private message but if you are not so far I'll come out for free because I am nice that way (laughing) and have a look in the cavity with a photographic endoscope / a chat from somebody who is not going to flog you anything. All the best, David Aldred

David - sorry to hijack the thread but do you have any advice/idea as to cavity wall insulation and external wall vents

David_Aldred

Hi Joyciebird,
Please do a search on here for the phrase cavity wall insulation and I have posted something there recently. However if you are still struggling please explain what your concerns are regarding wall vents and what your concerns are regarding cavity wall insulation and I will do my best to answer your query. Kindest regards, David Aldred independent damp and timber surveyor

joyciebird

David_Aldred wrote: »

Hi Joyciebird,
Please do a search on here for the phrase cavity wall insulation and I have posted something there recently. However if you are still struggling please explain what your concerns are regarding wall vents and what your concerns are regarding cavity wall insulation and I will do my best to answer your query. Kindest regards, David Aldred independent damp and timber surveyor

Believe me I have searched and searched but I am still at a loss.

Hiillserve have been round to survey my walls for cavity insulation. they have refused to do the insulation because of the vents.

The first vent I understand that they wont sleeve it because it is behind a drainpipe, but my brother fits gutting for a living so it can be moved no problem, they have agreed once this is done that vent is no longer an issue. The problem is the other vent. Its a vent to ensure the circulation on air to the wooden floor boards (I dont have any fires on the house), They say they cannot sleeve this but will not give me a reason why.

Please please help

David_Aldred

Hi Joyciebird,
Thanks for the response so here goes:

I see from your profile that you are located in Fleetwood and living less than 5 miles from you I can tell you we are both living virtually next to the Irish Sea and classed as living in an area of severe exposure. For this reason alone I would not recommend attempting to put full fill cavity wall insulation into your home as the risk of increased dampness from attempting to insert cavity wall insulation to homes in areas of severe exposure is high. I have literally looked into several thousand wall cavities with photographic endoscopes over many many years, all over the UK and obviously where you and I both live and many of these cavities have been cavity wall insulated so this statement is made from experience of seeing wet cavity wall insulation and not a hypothetical statement from academic with no practical experience of the subject matter.

You can put cavity wall insulation into such homes with severe exposure and you be lucky enough to get away with it but it will be entirely at your own risk and once it is in, if you do have problems it is not the easiest thing to remove. There are several companies who install cavity wall insulation to properties within areas of severe exposure and simply take the view that the % of those that complain is far less than those they make a profit from so it remains financially lucrative to them obviously helped by government grants, care and repair, help the aged etc who all push for increased fuel savings.

The suspended timber floor is obviously made of wood and wet / dry rot spores are in the air all the time. These spores are looking for oxygen, a certain temperature range, water and wood to germinate and grow. Since wood is plentiful in a house and the temperature / oxygen is appropriate the only thing that can be realistically controlled is the water. Timber will start to germinate such decay spores from the air at around 28% moisture content but will sustain that decay down to around 20-22%. The aim therefore is to keep the moisture of wood below 20% at which point decay will not occur or if it has occurred it will cease. Forget chemical preservatives other than spport measures it is this moisture content of the wood that is the key to why timber does or does not decay.

Most sub floor voids under suspended timber floors where you and I live have damp / wet soil / sand beneath them and they therefore rely heavily upon the wall vents to take this moisture laden air away from beneath the floors before the wood becomes damp and consequentially decays. Hence the cavity wall insulation installer has to ensure that their product does not block these vents, so they take the vents out, place dams around the vent inside the cavity to hold the insulation back and then replace the vent.

Some contractors forget or run out of dams to wall vents that the timber floor relies upon and the insulation then blocks the vents resulting in decay of the floors. Some insulation can pour into the adjoining property if no effective barrier is in place and cause them dampness problems that the owner of the subject property may be liable for.

The cavity wall insulation installer is looking for what condition the cavity is in, the moisture content of the timber floors, any history of dampness to the property, the location of the property, whether evaporation outwards from the wall is poor, the condition of the cavity wall ties, if there is significant debris within the cavity wall etc and if they are not happy with what they see then they should not recommend installation.

The cavity wall insulation product is inserted blindly - that is to say they only have a very rough idea by inserting an endoscope here and there (and some don't even do that) as to whether the insulation has fully filled the cavity. It is inherent that not all areas of the cavity will be filled and some cavity wall insulation slumps over time. In both cases voids are created that are prone to chronic condensation.

Cavity wall tie corrosion is an issue especially in properties classed as severe exposure. Cavity wall insulation tends to make the cavity wetter than it was previously (see below) and this accelerates cavity wall tie corrosion. Installing new cavity wall ties is done by hammer drilling that regulalrly breaks the back of the brick off the outer leaf of the cavity wall and this debris sits upon the cavity wall insulation giving a pathway to penetrating dampness. Removing or isolating original cavity wall ties to a wall that has been cavity wall insulated is a nightmare since it requires brick removal and depending upon the type of insulation, the loose fill can come streaming out of the wall when opened up. The insulation has to be made good before the brick can be put back which is not at all easy and often fails to be done adeqautely again resulting in increased dampenss.

Prior to cavity wall insulation air moves freely within the cavity of the wall. After cavity wall insulation is inserted of a full fill type, the movement of air does not stop but it is significantly reduced. In addition there is a significant temperature drop within the cavity on the cold side of the insulation. This combination of reduced air movement and temperature drop is not surprisingly a recipe for condensation especially where there are strong winds that will tend to take the heat out of the wall.

Properties classed as severe exposure are prone to penetrating dampness and the half brick skin of the outer leaf of the cavity wall is often of inadequate thickness to hold back wind driven rain, especially where there is stormy weather, considerable pressure differences between the outside of the building and inside of the cavity. I have seen rainwater literally running down the inside face of the outer leaf of the cavity wall many times during wind driven rain. If this moisture cannot get out and you fill te cavity with a fibre, chip or foam material it doesn't take a genius to work out where this moisture is going to end up.

If the property has a hard dense facing brick, has had its breathable lime mortar re-pointed in a hard dense cement mortar or had its lime render replaced with a hard dense cement render then evaporation outwards is considerably reduced and the easier option for moisture within the cavity wall is to permeate inwards. This can actually be made worse by sunshine upon the outer face of the wall driving the moisture inwards known as summer or reverse condensation.

To properties that are coastal wind blown sand tends to be in the air and on the wind it enters the cavity of the wall and roof voids. Within the cavity of walls this sand swirls around and erodes the hidden faces of brickwork and stonework within the cavity void. This sand and eroded debris compromises the cavity of the wall and can make it semi solid over lintels and at the base of the wall and on top of wall ties. These areas are colder than the rest of the wall especially where not insulated and prone to condensation / penetrating dampness.

It may therefore be seen from the above that to a property classed as severe exposure, condensation and penetrating dampness within the depth of the wall is a significant factor and that this is only exacerbated by attempting to blindly put into the wall cavity full fill insulation.

If the condensate and penetrating dampness cannot evaporate externally it will tend to migrate internally. Brickwork that is coastal tends to be contaminated by chlorides. As the moisture within the wall evaporates inwards it brings with it these chloride salts which contaminate the plaster. Salt contaminated plaster will attract moisture to it from the air in the room the same way leaving salt in a kitchen becomes damp and the plaster then is excessively hygroscopic and becomes constantly damp. Such plaster will not recover.

This issue of salts is compounded to properties in Fleetwood that were flooded by the sea in 1927 and some properties again in 1976-77. Where such properties were subject to sea water flooding - some to well over 1m deep this salt has been a constant problem to properties in Fleetwood for all these years and is often misdaignosed as failure of the damp proof proof course.

From my own experience out of all the different types of cavity wall insulation I see, the polystyrene chip / ball probably has the least dampenss problems but is certainly not free of issues. My persoanl experience suggests the foam and blown fibre seem particularly troublesome. Cavity wall insulation can be removed but this is not easy to do and is destructive requiring scaffolding and opening up of the wall in many areas.

There are alternatives to insulating walls other than cavity wall insulation such as internal insulated dry linings with appropriate vapour barriers or insulated renders / slabs some of which can have the appearance of brickwork.

Not an axhaustive explanation of things but hope this helps some of the issues and consequences. As I say, you pays your money and you takes your choice. Some people cavity wall insulate their homes on the back of advice from those selling it to properties in severe exposure and get away with it. For others it is the worst thing they ever did and the chronic dampness, degrading plaster and finishes becomes a complete nightmare of which the cavity wall insulater usually denies liability and is only prepared to make good any voids to the insulation that the client can point out. Kindest regards, David Aldred independent dampness, timber and cavity wall tie surveyor.

joyciebird

David

Thanks for this, after your very informative response we have decided that Cavity Wall is not for us.

We are going to go with the loft insulation that we have been offered (unless you have any advice against this), and look at other options to insulate the house.

You are right about being in an exposed area, we live just off the promenade and as an end terraced house, the wind and rain hits us from all angles.

THANKS VERY MUCH

Lisa