Single skin external wall- How to strengthen!!??

[itsdave]

Hi,

we are planning a 2 storey extension on the side of our semi-detached cottage which was built around 1900.

The external side wall is currently 'single skin' 4.5inch thick brick on both floors, rendered, and insulated in the inside. The wall measures about 5m x 4.2m high to the guttering level of the roof.

Once the extension is built (using a cavity wall) this single skin wall will become and internal wall.

We know we are likely going to have to strengthen the single skin wall, and a builder has suggested building a second skin outside of the existing wall and securing the two using wall ties. He said this would have to be the full height of the existing wall, with a foundation dug for the second skin of 1m.

Is it correct that now that the wall would be internal it needs such extensive strengthening? Would it be possible to strengthen the ground floor wall and not the first floor or is this pointless?

Does anyone have any alternative methods which we could discuss with an engineer which may be easier to achieve, such as using steel to increase strength/support?

We just want to make sure the house is mortgageable when we come to sell it. We are prepared to pay for the second skin method, but don't want to commit to such an expense before investigating alternatives!!

Thanks in advance for any guidance.

 

[Static]

Will the wall be load bearing?

 

[itsdave]

Will the wall be load bearing?

The wall is currently load bearing as it supports the floors and roof of the existing house. I have had a quick look at building regs for structures and to someone who has never seen these before, they appear to suggest that the extension could be built and only require 3 walls to be deemed load bearing. As such the extension should be able to be completed without adding additional load on the the wall.

 

[tony1851]

If it is going to end up as an internal wall, why is it necessary to strengthen it?

 

[freddiemercurystwin]

I read this that the existing wall is external and is to remain external but with another floor/storey on top. But could be wrong ....

 

[^woody^]

I can't understand what is going on or why this wall needs strengthening

With these extensions you either use the wall and underpin, or remove the wall and put in new foundations to take the new first floor extension

If the wall stays, it can be insulated and drylined

 

[itsdave]

If it is going to end up as an internal wall, why is it necessary to strengthen it?

In its present state the house is not mortgageable with the majority of lenders as many of them have criteria which the valuers must follow which states a maximum % of load bearing walls which they are willing to accept as single skin construction being (4.5inch thick). Despite supporting the house since around 1900, in the current market lenders are still viewing the thin wall as not structurally sound and thus won't lend.

When we have carried out the extension, yes the wall will become internal, yet it will still be a load bearing wall and hence still potentially fall foul of mortgage lender criteria. As we are spending a lot of money on this project we need to make absolutely sure that the structure meets the lending requirements of the majority of mortgage providers so that it doesn't deter buyers.

I hope that explains it?

Thanks.

 

[itsdave]

I read this that the existing wall is external and is to remain external but with another floor/storey on top. But could be wrong ....

Hi,

No, the wall is currently the external side wall of this semi detached property. The extension we are planning would be on the side of the house, currently just paty of the garden, and will have a large lounge room downstairs and an extra bedroom upstairs. So from the roadside as you look at the house, its width would be almost doubled.

Does that help?

 

[itsdave]

I can't understand what is going on or why this wall needs strengthening

With these extensions you either use the wall and underpin, or remove the wall and put in new foundations to take the new first floor extension

If the wall stays, it can be insulated and drylined

Hi woody,

I have just responded to two other posts about the extension and why we are considering strengthening the wall, so I hope they explain what is going on.

With regard to the underpinning, it is not the foundation of the wall that has been called in to question by the mortgage lenders, but the thickness of the wall itself as they consider a 4.5inch thick wall not to be structurally sound. The wall is drylined and insulated at the moment as it is still an external wall. When we build the extension the wall will become internal.

Thanks.

 

[tony1851]

Are all the other walls in your house 4 1/2" brick - ie front and rear as well,
or is it just the side- and party walls? If you are building a side extension, the front, side and rear wall of the extension would presumably be in cavity wall.
Would this alone not make your structural situation better?

 

[itsdave]

Hi Tony,

There are two walls that are 4.5inch brick, the side and the rear wall. My post here only really asked about the side wall as this is the wall that would become internal with our extension.

You are right, the side extension will be built using a cavity wall construction.

I am not sure whether this would be sufficient or not, which is why I posted in this forum really to try and get some broader opinion.

We tried to get a mortgage on the property to buy it and were rejected because of the walls. We have since been lucky enough to be able to buy it for cash, but will need a mortgage in future. The valuer was saying that the lending criteria had a maximum proportion it would accept of 'Structural walls' that are 4.5inch. Given that even with the extension, the 4.5inch wall would still be structural I would just be very nervous of the house again being rejected if we did not carry out some work to the 4.5inch wall.

We have spoken to a couple of people with more experience than me and they said it should be fine, and that the valuers working for the mortgage lenders are just being stupid. But it would be one hell of a risk for me to just proceed with something which 'should be fine' only to find out it still isn't mortgageable because the valuers are still being 'stupid' about the wall.

In case anyone is interested, the Lender we were initially using was Leeds BS, although when this fell through I know our mortgage adviser contacted many others such as the Halifax, HSBC etc.

Cheers.

 

[tony1851]

Have any of these valuers actually given you a figure for the maximum allowable percentage of walls which are load-bearing and only 4.5" thick? Or is it related to the floor area of the house?
It seems to me like a straightforward maths problem, ie measuring the lengths of your walls and seeing how it would work out with your side extension taken into account.
One other point might be worth considering. It is quite rare for a house to have any external walls only 4.5" thick brick, particularly over two storeys.
Is it thisthat your valuers are on about, where perhaps the valuers have not made it clear to you, and that you are confusing 'loadbearing' with 'external'?
I would think any building society would be wary about giving a mortgage on a property with 4.5" brick external walls.
You really need to check this out as there may well be no point in doing any work on your existing side wall in view of the proposed extension.

 

[itsdave]

The figure differs from lender to lender and can change. Some allow 25%, some allow only 10%, some allow only on single storey elements of a house and some just refuse full stop. Our concern was improving it so that it is acceptable to most mainstream mortgages.

You are quite right about it being rare to have 4.5inch 2 storey external walls, and I had assumed that the problem was that they were external when I initially found out about it (that seems to be what is discussed in many other forums if you google it), but then the valuer made he distinction.

Seeing as what the valuer said seems to have been slightly different from what other people have experienced (and slightly different from your interpretation of what is usually the issue) I think it is worth ringing a few more surveyors and mortgage companies to find out precisely what the criteria is they apply to get some broader opinion.

Thanks again, I guess I need to get on the phone now then!