Additional cavity wall ties - what are they?

vegasvisitor

Hi

Just looked at a Scottish home report that mentinos additional cavity wall ties being added at the property. Anyone know what these are?

Also the property appears to be built on top of the railway tunnel (which has been there since the late 1800s, house is 1960s. Is this likely to be an issue? The tunnel runs right through our side of town between 2 stations, so I'm thinking there's lots of much older houses still standing! I've never known any local issues with this, and have never heard it mentioned in insurance quotes either.

mlz1413

As far as I'm aware all cavity walls need the ties, ie 2 walls are built and then tied together with metal straps, then the gap/cavity is filled with insulation.

Is there any evidence of movement in the walls? repointing of any areas? It sounds like more ties have been added but when and why haven't been specified, although the railway seems the most obvious reason.

Can you ask the EA or owners for more details?

vegasvisitor

Yes, will ask the owner if we go for a second viewing, also will be able to see the house in better light and look for evidence of cracking etc. It has a good structural scoring, category 1 being no repair needed.

The detail is:-

Insufficient ties in cavity walls. Work carried out 2000 by _____ as specified in BS 5628 part 1 1992.

Not really sure what the last part means. I suppose this is saying that there were just not enough ties, maybe movement was noted and that more were added. The house is mainly roughcast (stone at bottom), so I'm not sure what I will see. I will need to guess if the roughcast is new I suppose (it's not painted, so not something that could have been repaired and re-painted to cover it).

bosseyed

lesley74 wrote: »

Yes, will ask the owner if we go for a second viewing, also will be able to see the house in better light and look for evidence of cracking etc. It has a good structural scoring, category 1 being no repair needed.

The detail is:-

Insufficient ties in cavity walls. Work carried out 2000 by _____ as specified in BS 5628 part 1 1992.

Not really sure what the last part means. I suppose this is saying that there were just not enough ties, maybe movement was noted and that more were added. The house is mainly roughcast (stone at bottom), so I'm not sure what I will see. I will need to guess if the roughcast is new I suppose (it's not painted, so not something that could have been repaired and re-painted to cover it).

Wall ties are the metal bow tie shaped (generally, although they come in a variety of shapes and sizes) loops of thick wire that are built into the external leafs of a cavity wall when it is erected - essentially they 'tie' the two walls together across the cavity and make the whole thing structurally more solid.

I forget the precise requirements of the latest BS and it might have been different in 1992, but it basically states the minimum number of ties you need to install as the wall is built - usually something along the lines of a wall tie every 900mm apart horizontally and 450mm apart vertically. Like I say, thats from memory so may be wrong!

Running_Horse

I vaguely remember that ties from before a certain date (when building regs changed) tend to rust away, and any survey will insist they are replaced with modern ones. That may be what happened here.

David_Aldred

Hi,
Please see my previous posts on this forum regarding cavity wall ties / implications with cavity wall inulation. As previously indicated by the posts above the external walls where ties are fitted are known as cavity walls and consist of an outer wall, a cavity void and an inner wall. Typically in older traditional cavity walls but not always the outer wall (leaf) is half a brick thick and so is the inner wall. These two walls need to be tied together at regular intervals to be structurally stable and this was often but not always done with metal ties, typically galvanised or bitumen coated steel.

The spacing and pattern of the number of ties required became more rigorous over the years such that a considerable number of older cavity wall houses will not meet current Building Recommendations for the number and pattern of existing ties. Failure to meet this current number and pattern does not mean a house is suddenly going to collapse but obviously it is preferable for a property to comply with current wall tie spacing recommendations.

Of more concern however is that original ferrous cavity wall ties will corrode over time for a number of reasons. If the ties failed to hold the outer leaf onto the property it is at risk of collapse which can be sudden and dramatic usually in high winds and it should be obvious that an exposed large two or three storey gable end is more at risk of doing so than a small sheltered hipped roof bungalow.

The original ferrous ties come in various types and all will expand to several times their original volume as they delaminate with corrosion. Mortar is strong in compression but weak in tension. Small wire gauge ties may cause little disruption as they expand with corrosion but larger gauge and plate ties expanding with corrosion will crack open the mortar beds / render. Over the height of the wall the cumulative effect of expanding corroding large gauge wall ties is quite sufficient to lift roof plates, bulge walls and make the elevation as a whole structurally unstable.

From what you are saying a contractor has installed additional ties to the property. Whilst this is all well and good it would be prudent to check what type of original tie is present because large gauge / plate ties should be isolated / removed from the walls to prevent them causing the damage mentioned above. This works is considerably expensive, disruptive, requires scaffolding / safe working access, brick / render removal and making good which if not done to a high standard can be very unsightly. If cavity wall insulation has been fitted this obviously makes opening up the cavity wall and making good very difficult. You can see that this does need checking as the costs if necessary should be allowed for in your purchase negotiations.

Corroding cavity wall ties and remedial action recommended is discussed within Building Research Establishment (BRE) Digests 329 and 401 and upon reading these documents it should become clear that the protective coating to wall ties installed into a 1960's property would be expected to have have depleted and it is likely original ties are significantly corroded. This will be especially so if black ash type mortar has been used which was made from coal slag high in sulphates that accelerate ferrous cavity wall tie corrosion.

In conclusion therefore you need to know if cavity wal linsulation is present, what type of original ties are present and whether they need removing / isolating or if they are of a type that can be left within the wall to corrode. In addition that the replacement cavity wall ties are covered by a long term insurance backed guarantee that is transferable to yourself if you purchased the property. Hope this helps, kindest regards David Aldred Independent damp and timber surveyor

vegasvisitor

Many thanks that is much appreciated. It is indeed an exposed wall, I live in the same area as the house, and it is the same side as our 'eposed wall'.

This is strange because I was never aware of this and I have a 1940s 1/4 villa with cavity walls, so given that the house is 1960s and is a bungalow (with loft space used from start we were told), our house stands much taller on the walls, and its a larger overall building, less squarey more narrow from the side etc, so I would guess our own would be more at risk!

We're a bit in a quandry about what to do. Going back to view again over the weekend so will look at outside walls for evidence of disruption or replacement of rendering. The house is on for too high a price. Yes, it's detatched, but it's only 3 bedrooms, and there are other houses in the general area on the market at the same price but they all seem to be bigger or in better state of repair. In Scotland, and it does have a survey at the price, but I'm sort of not believing it. It has been on the market for just over a year too, so I'm thinking if noone else wants to pay the price for it, then it can't be worth that. They've only had a few viewers and no offers so I think that suggests that too.

David_Aldred

Hi again Lesley,
In all honesty the only way to know what is going on with the cavity wall ties is for somebody competant to have a look into the cavity either with an illuminated endoscope / boroscope preferably with a camera attached or by sample brick removal.

At one time this issue of cavity wall ties was firmly in the hands of structural engineers who would be asked to inspect when there was visible concern such as cracking of walls or bulging etc. However what happened was a few elevations started to collapse suddenly usually in stormy conditions without much of an external visible sign of things being amisss especially if the wall tie type was a small gauge wire that would not necessarily show much cracking to the surrounding masonry.

As you can imagine the potential for injury / damage is huge along with the liability to the building insurers. Because of this the BRE amongst others were asked to look into this and it was found that ties would corrode most within the outer leaf mortar beds at high exposed levels more than within the cavity which in turn would corrode more than within the inner leaf as a general rule.

Given it was impractical to determine exactly when a tie was about to suddenly fail especially in stormy weather when air pressure on either side of the outer leaf of the wall can fluctuate rapidly known as wind pumping the only recommendation was to install new ties when existing were seen to be rusty and address large gauge / section ties if they were of a type that would cause damge to masonry / the building as a whole as they continued to expand with corrosion.

It has to be said that the majority of the UK housing stock is affected especially when in their wisdom the amount of galvanising applied to wall ties as a protective layer was reduced in 1970's / early 80's until it was realised this was leading to premature failure. Galvanised ties became less popular in recent times despite increasing the protective layer and the majority of new ties these days are stainless steel although even these can have problems under certain circumstances.

One of the interesting things to happen was the remedial treatment contractors who were undertaking dpc work and woodworm / rot treatments saw the oppertunity to add cavity wall tie work to their services especially as the cost of the work when it first started to appear was quite lucrative although these days prices have actually tended to drop because there are so many contractors now doing the work. Armed with the BRE digest recommendations there was a shift from the structural engineer saying whether a wall needed to have wall tie work to placing the inspection and decision for that work in the hands of those making a profit from such work. The client can have a contractor check the ties or they can have an independent specialist surveyor inspect the ties or they can have a structural engineer if they have the equipment inspect the ties. The choice is yours.

As with all things there are good and bad contractors and some contractors will give an honest opinion about whether ties need to be replaced / existing ties addressed and others who are obviously cowboys out for a quick buck. Just because ties have been inserted does not mean that they are necessarily holding the wall together properly and there have been quite a few cases of walls that have been re-tied still moving and having to be rebuilt. Most guarantees offered are a product guarantee only that is to say only guarantee the tie is fit for purpose and not that the wall will not collapse which is an important difference.

There are clearly benefits to having somebody who is not the contractor who put the ties in (in other words a third party) inspect the work and test sample ties to see if they are actually doing their job and that any large section ties have been removed. It would not be the first time folk have drilled the holes but not put the ties in / not addressed exisiting ties where necessary.

The drilling often causes debris to fall into the cavity and this should be removed where it may lead to bridging of the cavity or compromising the damp proof course if it falls to the bottom. The size of the debris can be large as the hammer drilling may break away the back of the outer leaf of brickwork. This can be a major problem when undertaking wall tie work to cavities that have been insulated leading to patch areas of penetrating dampness / cold spots prone to condensation across the cavity.

One point of note is that contractors used to put in new ties from ladders and take any old ties out by scaffolding / safe working platform. The Work at Height Regulations 2005 really made installing cavity wall ties from ladders a dodgy practice and if somebody had an accident and it was shown a safer means of working platform (i.e scaffolding or hydraulic platform) could have been used then there is a case for liability.

This liability may not only extend to the contractor's boss it may also have the potential to extend to the person who's house it is / the person who is paying for the work to be done. The contractor is in a difficult situation here because if they quote to scaffold they may not be competitive with those that quote for doing the work from ladders yet if there is an accident they may well along with those paying for the work be in the poo. This is typical of the construction industry and why people continue to get killed / injured every year through cutting corners usually to win contracts.

The mortgage companies clearly want new ties in properties / existing ties addressed where necessary on a basis of this being a rolling program of repairs to UK housing stock as and when properties come up for sale and it would be a reckless surveyor who did not mention cavity wall ties to be inspected as a general comment given the potential for liability. Of concern are houses that slip through the resale net where the ties will corrode to the point of failure until the outer leaf suddenly falls off onto anything and anyone below.

This will become more and more of an issue the older the properties become and rather like the asbestos problems there may well be a peak in failures the like of which we have not yet seen. In addition you should be aware that this applies to large commercial buildings including schools etc just as much as domestic housing stock and sooner or later somebody is likley to get killed at which point there may well be a panic to do more.

As regards the domestic housing then small low height "box like" construction of some properties is a saving feature in that even with failed ties some properties will still be relatively stable but this does not apply to all such housing especially as I said with large gables or say a terraced property where there is a long run of brickwork.

The spacing of ties required depends upon the width of the cavity, the construction and height of the property. Additional ties are required at weak points around openings such as windows and doors. Hope this helps, kindest regards, David Aldred Independent Surveyor

~moneysavingnovice~

David_Aldred wrote: »

Hi again Lesley,
In all honesty the only way to know what is going on with the cavity wall ties is for somebody competant to have a look into the cavity either with an illuminated endoscope / boroscope preferably with a camera attached or by sample brick removal.

At one time this issue of cavity wall ties was firmly in the hands of structural engineers who would be asked to inspect when there was visible concern such as cracking of walls or bulging etc. However what happened was a few elevations started to collapse suddenly usually in stormy conditions without much of an external visible sign of things being amisss especially if the wall tie type was a small gauge wire that would not necessarily show much cracking to the surrounding masonry.

As you can imagine the potential for injury / damage is huge along with the liability to the building insurers. Because of this the BRE amongst others were asked to look into this and it was found that ties would corrode most within the outer leaf mortar beds at high exposed levels more than within the cavity which in turn would corrode more than within the inner leaf as a general rule.

Given it was impractical to determine exactly when a tie was about to suddenly fail especially in stormy weather when air pressure on either side of the outer leaf of the wall can fluctuate rapidly known as wind pumping the only recommendation was to install new ties when existing were seen to be rusty and address large gauge / section ties if they were of a type that would cause damge to masonry / the building as a whole as they continued to expand with corrosion.

It has to be said that the majority of the UK housing stock is affected especially when in their wisdom the amount of galvanising applied to wall ties as a protective layer was reduced in 1970's / early 80's until it was realised this was leading to premature failure. Galvanised ties became less popular in recent times despite increasing the protective layer and the majority of new ties these days are stainless steel although even these can have problems under certain circumstances.

One of the interesting things to happen was the remedial treatment contractors who were undertaking dpc work and woodworm / rot treatments saw the oppertunity to add cavity wall tie work to their services especially as the cost of the work when it first started to appear was quite lucrative although these days prices have actually tended to drop because there are so many contractors now doing the work. Armed with the BRE digest recommendations there was a shift from the structural engineer saying whether a wall needed to have wall tie work to placing the inspection and decision for that work in the hands of those making a profit from such work. The client can have a contractor check the ties or they can have an independent specialist surveyor inspect the ties or they can have a structural engineer if they have the equipment inspect the ties. The choice is yours.

As with all things there are good and bad contractors and some contractors will give an honest opinion about whether ties need to be replaced / existing ties addressed and others who are obviously cowboys out for a quick buck. Just because ties have been inserted does not mean that they are necessarily holding the wall together properly and there have been quite a few cases of walls that have been re-tied still moving and having to be rebuilt. Most guarantees offered are a product guarantee only that is to say only guarantee the tie is fit for purpose and not that the wall will not collapse which is an important difference.

There are clearly benefits to having somebody who is not the contractor who put the ties in (in other words a third party) inspect the work and test sample ties to see if they are actually doing their job and that any large section ties have been removed. It would not be the first time folk have drilled the holes but not put the ties in / not addressed exisiting ties where necessary.

The drilling often causes debris to fall into the cavity and this should be removed where it may lead to bridging of the cavity or compromising the damp proof course if it falls to the bottom. The size of the debris can be large as the hammer drilling may break away the back of the outer leaf of brickwork. This can be a major problem when undertaking wall tie work to cavities that have been insulated leading to patch areas of penetrating dampness / cold spots prone to condensation across the cavity.

One point of note is that contractors used to put in new ties from ladders and take any old ties out by scaffolding / safe working platform. The Work at Height Regulations 2005 really made installing cavity wall ties from ladders a dodgy practice and if somebody had an accident and it was shown a safer means of working platform (i.e scaffolding or hydraulic platform) could have been used then there is a case for liability.

This liability may not only extend to the contractor's boss it may also have the potential to extend to the person who's house it is / the person who is paying for the work to be done. The contractor is in a difficult situation here because if they quote to scaffold they may not be competitive with those that quote for doing the work from ladders yet if there is an accident they may well along with those paying for the work be in the poo. This is typical of the construction industry and why people continue to get killed / injured every year through cutting corners usually to win contracts.

The mortgage companies clearly want new ties in properties / existing ties addressed where necessary on a basis of this being a rolling program of repairs to UK housing stock as and when properties come up for sale and it would be a reckless surveyor who did not mention cavity wall ties to be inspected as a general comment given the potential for liability. Of concern are houses that slip through the resale net where the ties will corrode to the point of failure until the outer leaf suddenly falls off onto anything and anyone below.

This will become more and more of an issue the older the properties become and rather like the asbestos problems there may well be a peak in failures the like of which we have not yet seen. In addition you should be aware that this applies to large commercial buildings including schools etc just as much as domestic housing stock and sooner or later somebody is likley to get killed at which point there may well be a panic to do more.

As regards the domestic housing then small low height "box like" construction of some properties is a saving feature in that even with failed ties some properties will still be relatively stable but this does not apply to all such housing especially as I said with large gables or say a terraced property where there is a long run of brickwork.

The spacing of ties required depends upon the width of the cavity, the construction and height of the property. Additional ties are required at weak points around openings such as windows and doors. Hope this helps, kindest regards, David Aldred Independent Surveyor

Hi David, not sure if you're still around and can help me (or anyone else can).

I'm about to buy my first house, a Victorian flat, end of terrace. However, on the end wall, there are 4 white disks. A friend of mine has suggested these are probably the end of wall ties used to stop the walls bowing. This has really worried me- even if they don't need replacing, will they affect the saleability of the property in the future??

Mankysteve

If its had replacement wall ties installed, There be small round holes drilled all over the building usually filled in a filler to ,match brick colour or at least that how it is on my parents house.

David_Aldred

Hi moneysavingnovice,
From what you are describing I would guess at these not being standard cavity wall ties but the large cast plates with tie bars sometimes with externally visible large bolts and nuts seen on many properties of this age and type used as a method of lateral restraint. They come in various forms and sometimes the spreader plates (to increase the area of restraint) themselves can be very ornate especially those dating back over a hundred years. The way they tie the building together also varies considerably depending upon the reason they were fitted and indeed soem are fitted during initial construction rather than as part of any repair works though obviously the latter also applies in some cases. With regard to your query as to whether you need to be concerned about them? Well they are there for a reason of structural restraint and accordingly your surveyor should be asked to comment upon why they presume they were installed and whether their installation remains affective. Hope this is of use. Kindest regards, David Aldred Independent damp, cavity wall tie and timber surveyor.