Rebuilding outer leaf

[Jilly]

I’m guessing external insulation wouldn’t work?

[BotusBuild]

11 minutes ago, Jilly said:

I’m guessing external insulation wouldn’t work?

I can't see why not. I think it's been suggested already. 

[Gus Potter]

3 hours ago, Iceverge said:

I'll reiterate my point buried in my earlier post. 

 

The worse thing that any self builder can do is value their time at zero. 

 

You need to put a £ figure on every hour you spend on site. Say £20. 

 

 

Re taking down the leaf of a cavity wall. @Gus Potter and @saveasteading might be along to discuss why this is a bad idea. 

 

As far as I understand the two leafs when ties together act more like a wide solid wall, like a "H" rugby goals. 

 

When you take away half almost all of the lateral strength disappears.

Good advice.

 

In a standard cavity wall (say 50-75mm cavity) the two leaves act together. When doing calculations we derive an effective thickness of the wall. A bit like this bit from the the BS code. But the strength of the wall as @Iceverge say rapidly decreases exponentially the thinner the effective thickness.

 

There are other kinds of masonry walls. Solid walls are say built with English Garden bond. These you can't really take down the inner skin in any practical way. There is  a wall called a collar jointed wall. Here the cavity is no more than 25mm and fully filled with mortar. One key thing here (collar wall) is that the wall ties are much thicker and more robust. Ancon do a wall tie for collar jointed walls. A collar wall tied with the right ties acts like a solid wall so you get more bang for your buck.

 

 

It's a good idea to value you time. £20.00 per hour seems reasonable. That's £160 a day. A trade rate up near Glasgow can vary from say £100-120 a day for an inexperienced labourer up to say 220 - 250 a day for a good experienced joiner( chippie)... more for a spark and techy folk. Now if that is all through the books and you are doing an extension there may be vat and an extra contractor profit / overheads to go on top of that.

 

When you look at it this way it can be good or bad! If your time spent on site is doing some work then you win a watch. You efforts are tax free and not subject to contractor profit for example. Any time spent keeping an eye on the builder is still worth while as it can head off disputes and extra claims for cost later on. It can help keep the quality of workmanship up too.

 

 

 

 

 

 

 

 

 

 

[Mike]

7 hours ago, allthatpebbledash said:

Hardly makes sense to knock it down to save further 5% on the tax considering cost of JCB and new foundations. My only issue is the pebbledash, maybe I should just own it? Paint it white, dash showing and all?

It's not just the VAT. I've undertaken several deep renovations myself, as well as having managed & priced them commercially, and they always turns out to be more expensive than rebuilding would have been - unless you're doing much of the work & discounting the cost of your labour.

 

In addition to strip-out costs, many things just take more time and/or cost more. For example, building a doorway into a new internal wall is more-or-less 'free' - the extra costs are roughly balanced out by saving 1.5m² of blockwork. On the other hand, knocking a hole through an existing wall, well that's a couple of days work + additional materials. Then there are things you find that you didn't expect that need fixing - walls, floors & ceilings out of level; botched DIY; sagging rafters; dry-rot; lead water mains; cracked sewers, whatever - which also takes more time to fix than fitting from new. And making an old house properly airtight - which is highly recommended - is almost always more complex because it wasn't considered as part of the original design.

 

There are good reasons for not demolishing. Maybe you just want to tart it up & flip it. Maybe you need to live in it because you have nowhere else and a caravan is out. Maybe the building has a particular heritage value (whether listed or not). Or, as with my current project, maybe it's an apartment - which kind of rules out demolition!

 

But if you do decide to renovate then do make sure that includes a thermal upgrade to at least Building Regs standards. Better than that if you're concerned about future energy costs and / the future additional value that it's likely to provide.

[Iceverge]

I cannot emphasis this enough. There'll always be more work to do than one person can manage and you need a metric to value your time. £ or € or $ is a pretty good one. 

 

Let me give you some examples. 

 

I stupidly chased our walls with a 9" grinder ( because I had it) rather than pay €120 for a days rental of the proper tools. 

 

It took me about 20 hrs of pure torture. 

 

My mate rented the machine and did his house in an afternoon. At €20/hr it stupidly cost me double what his did. 

 

I can lay blocks, but I'm slow and I don't like doing it for more than a couple of hours as I'm too soft. I reckon about 10/hr would be average. That come to about €2/block. Maybe that makes some sense for small projects but no way for a large house. 

 

Gains can be made where you do the donkey work of someone who's more highly skilled. Like UFH pipe laying or pulling cables for wiring. Plumbers and sparkles are expensive laborers. 

 

Another example, my mate, extended a cottage. 4 men took 2 days to crowbar and sledge down an old stone chimney. All unpaid, family, mates etc. then they took the same again to break out the old floor. Then the same to take off the roof. 

 

Had they hired a digger and demoed the house their mate time could probably have saved them multiples of the cost later in the build. 

 

 

 

 

 

 

 

 

 

 

[Iceverge]

4 minutes ago, Iceverge said:

I cannot emphasis this enough. There'll always be more work to do than one person can manage and you need a metric to value your time. £ or € or $ is a pretty good one. 

 

Let me give you some examples. 

 

I stupidly chased our walls with a 9" grinder ( because I had it) rather than pay €120 for a days rental of the proper tools. 

 

It took me about 20 hrs of pure torture. 

 

My mate rented the machine and did his house in an afternoon. At €20/hr it stupidly cost me double what his did. 

 

I can lay blocks, but I'm slow and I don't like doing it for more than a couple of hours as I'm too soft. I reckon about 10/hr would be average. That come to about €2/block. Maybe that makes some sense for small projects but no way for a large house. 

 

Gains can be made where you do the donkey work of someone who's more highly skilled. Like UFH pipe laying or pulling cables for wiring. Plumbers and sparkles are expensive laborers. 

 

Another example, my mate, extended a cottage. 4 men took 2 days to crowbar and sledge down an old stone chimney. All unpaid, family, mates etc. then they took the same again to break out the old floor. Then the same to take off the roof. 

 

Had they hired a digger and demoed the house their mate time could probably have saved them multiples of the cost later in the build. 

 

 

 

 

 

 

 

 

 

 

 

 

I helped my mate for free with the build, pouring concrete, groundworks, airtighess and some basic carpentry. 

 

I didn't do any of the fooling with the manual demolition though. I've learned the long way my time isn't worthless. 

 

I did offer to drive my digger straight through it though. 

Edited Wednesday at 22:24 by Iceverge

[allthatpebbledash]

19 hours ago, crispy_wafer said:

Just popping in to say, a neighbour down the road from me refurbed his bungalow last year, roof off, external block and render away, bricked the outer leaf and did an internal refit too and a smallish extension.  Took him 4 - 6 months, but is a builder by trade, so has the benefits of can do, or knows men who can.  

Interesting. That’s 2 I’ve read about now saying it can be done.

 

17 hours ago, Russell griffiths said:

@allthatpebbledash I’m just trying to be a realist

your saying a knock down and rebuild will be more expensive, it certainly will be, but how much better will the final product be, and what is the value of a new build versus your refurbishment. 
 

get some nice street scene pictures done for you and get them valued, you might be surprised how much the new build comes out at. 
 

having spent all my life chopping houses about before I found one to knock down, I will never do a refurbishment again. 
 

if it’s been empty two years I can guess what sort of condition it’s in. 
 

 

 

For it being empty, I bought it as long term family home. Never moved in as we planned a remodel. But then remodel came in pricey with not much space gained so I went in with an application for a full demo and rebuild, but larger footprint. The planners were having none of it. I either rebuild to same footprint more or less, or refurb it. So now I’m back at refurb. But this time plans are to retain almost all the walls, and extend at the rear.

 

Time since purchased to now is just over 2 years now. The property is in good condition, it got stripped out after application 1 got approved and the structural engineer wanted to understand make up of existing walls. This is why it’s sat as a shell now, everything needs putting back in.

 

The future value in this is irrelevant to the discussion. I don’t plan on selling.

 

17 hours ago, Russell griffiths said:

What sort of insulation levels would a refurbishment of this kind need to comply with building regs. 
 

if you take down the outer leaf and extend the cavity to get 100mm of batts inside it then what happens with the wall ties, are they not going to be too short, then what about the lintels, then will this wider wall fit on the footings with the new regs on footing width. 

I was thinking the leaf would sit at same width so footings remind same, and you’d use batts that are 75mm to fit existing cavity?

 

17 hours ago, Canski said:

Oh thanks. I can’t bring myself to build them for a loss. Maybe the same applies to the OP. We all know it would be a better house if demolished and rebuilt but I doubt if the numbers would add up.

 

This is where I got stuck. I previously did look at demo and new build, but the planners wanted it to be same footprint near enough. I couldn’t overcome the cost of demo, new footings, only for house to be of same size? 
 

That’s not including the fact if I go back in now to say we will demo and rebuild as planned for the refurb, the application would take another 12 months? 
 

17 hours ago, saveasteading said:

 

Correct. The strength of  a single skin is much less than half of the double skin.  It would need temporary support during the work. THe support gets in the way.

You would not live in the house while this was happening, and should move heavy furniture out.

A new outer skin could be tied using brackets screwed to the inner wall: that is the least of your issues.

 

It's not only structure though.

Do not ignore the detailing at the foundation ( does the widened wall fit on it still?)

Or at the roof. How does this new outer face line work with the current eave and gutter...you probably have to extend the roof at eaves and gable.?

And at doors and windows?

 

I wouldn't dream of doing this. Not with my house and my money anyway.

New roof going on. Can be put on same footings so no increase in cavity? If few sections at a time are put on support, built up, and move along to next, surely it’s possible? All new windows and doors, lintels, and ground plus intermediate floor. Does this change things?

 

11 hours ago, Iceverge said:

I cannot emphasis this enough. There'll always be more work to do than one person can manage and you need a metric to value your time. £ or € or $ is a pretty good one. 

 

Let me give you some examples. 

 

I stupidly chased our walls with a 9" grinder ( because I had it) rather than pay €120 for a days rental of the proper tools. 

 

It took me about 20 hrs of pure torture. 

 

My mate rented the machine and did his house in an afternoon. At €20/hr it stupidly cost me double what his did. 

 

I can lay blocks, but I'm slow and I don't like doing it for more than a couple of hours as I'm too soft. I reckon about 10/hr would be average. That come to about €2/block. Maybe that makes some sense for small projects but no way for a large house. 

 

Gains can be made where you do the donkey work of someone who's more highly skilled. Like UFH pipe laying or pulling cables for wiring. Plumbers and sparkles are expensive laborers. 

 

Another example, my mate, extended a cottage. 4 men took 2 days to crowbar and sledge down an old stone chimney. All unpaid, family, mates etc. then they took the same again to break out the old floor. Then the same to take off the roof. 

 

Had they hired a digger and demoed the house their mate time could probably have saved them multiples of the cost later in the build. 

 

 

 

 

 

 

 

 

 

 

 

 

Great advice once again lad.

 

Here’s how I’m looking at it.

 

Currently it’s sat as a shell.

Everything needs putting back in.

Planning approval for refurb only.

Tax at 5% or nil rated for some items.

New build application would take another 12 months or so, I presume.

Cost of demo/excavations and new foundations I estimate will be high in current climate.

Existing masonry shell probably has a built value of £100k at least.

To demo (circa £20k), new foundations (circa 40k, based on nearby friends build).

 

I’m effectively looking at £200k cost to get back to where it stands now? Or have I missed something?

 

[saveasteading]

12 hours ago, Mike said:

But if you do decide to renovate

What a good summary. Save it  for future discussions on the subject.

 

In brief? A biggish business would demolish. A little builder might do a cheap tart up and pretend to live in it, a real diy can look after details and quality, and phase the work with lots of disruption. It is about cash flow.

[Iceverge]

Any pics to see what you're dealing with? 

 

The strip out and trouble you've gone to with planning thus far might lead you down the sunk cost fallacy. Beware. 

 

 

 

 

[lookseehear]

Shouldn't there be some consideration for the carbon implications of demolish and rebuild? It's difficult for the average person to quantify but it definitely was a factor when we looked at this. There's some legitimacy to the idea that you shouldn't knock down a structure that is otherwise sound. It isn't always all about the pounds and pence, particularly given there's uncertainty whatever route you go down.

[Mike]

8 hours ago, allthatpebbledash said:

I either rebuild to same footprint more or less

Though you may be able to add useful m² by building a basement, subject to permission.

 

8 hours ago, allthatpebbledash said:

New build application would take another 12 months or so, I presume.

Theoretically 8 weeks from submission, but you'd need to check out other local applications to get an idea of the reality.

 

4 hours ago, lookseehear said:

Shouldn't there be some consideration for the carbon implications of demolish and rebuild? ...There's some legitimacy to the idea that you shouldn't knock down a structure that is otherwise sound

Yes, that is a factor, but a difficult one.

[allthatpebbledash]

21 hours ago, Iceverge said:

Any pics to see what you're dealing with? 

 

The strip out and trouble you've gone to with planning thus far might lead you down the sunk cost fallacy. Beware. 

 

 

 

 

Yeah lots, anything specific you want to see or just elevations?

 

What’s the sunk cost fallacy? 
 

What about building a third leaf creating 2 wall cavity’s that are filled?

 

14 hours ago, Mike said:

Though you may be able to add useful m² by building a basement, subject to permission.

 

Theoretically 8 weeks from submission, but you'd need to check out other local applications to get an idea of the reality.

 

Yes, that is a factor, but a difficult one.

Basement was an option early on, but we decided against it.

 

As for the new build planning, I already floated one application of a new build through the council. They wanted a CMRA which is fine, but then comments from biodiversity department were suggesting they request a bat survey prior to even any consideration of looking at the application. According to a neighbour friend of mine, it can take months to have one completed, theirs had taken 30 weeks!

 

18 hours ago, lookseehear said:

Shouldn't there be some consideration for the carbon implications of demolish and rebuild? It's difficult for the average person to quantify but it definitely was a factor when we looked at this. There's some legitimacy to the idea that you shouldn't knock down a structure that is otherwise sound. It isn't always all about the pounds and pence, particularly given there's uncertainty whatever route you go down.

 

I think it actually always is about the pounds and pennies. The carbon implication conversation is just a calling card at election campaigns.

 

If not, the government would be incentivising retrofit applications as opposed to nil rating the demos and rebuilds only. Given the majority of the populous I believe only extend and renovate and pay full VAT for doing so means more cash in the kitty. 

 

22 hours ago, saveasteading said:

What a good summary. Save it  for future discussions on the subject.

 

In brief? A biggish business would demolish. A little builder might do a cheap tart up and pretend to live in it, a real diy can look after details and quality, and phase the work with lots of disruption. It is about cash flow.

True.

 

Okay so yesterday I happened across an old episode of grand designs. Maybe taking down the external leaf and rebuilding it is a terrible idea, but building a third leaf is a better one?

 

Already spoken to the engineer who’s done this and the house in question is a beautiful award winning house.

 

Here’s the idea.

 

Increase width of foundations. As we need some underpinning in areas as it is, this can be done as part of the works. Then, build a third leaf of facing brick, insulation in the now 2nd wall cavity, which gives a more better insulated and air tight external wall. What is the opinion on this?

 

[Mike]

1 hour ago, allthatpebbledash said:

Increase width of foundations. Then, build a third leaf of facing brick, insulation in the now 2nd wall cavity, which gives a more better insulated and air tight external wall. What is the opinion on this?

It's possible, but what's the advantage over your option 3 (Leave pebbledash in situ, inspect to make sure no cracks etc, fix EWI straight on top and render over)? Just seems to be adding unnecessary additional cost.

 

 

2 hours ago, allthatpebbledash said:

As we need some underpinning in areas as it is

Then that's another big tick in favour of rebuilding - underpinning isn't cheap and it's presence (especially if because of subsidence) may add to the cost of house insurance and put off potential future buyers.

[saveasteading]

35 minutes ago, Mike said:

underpinning isn't cheap 

Somebody will be more up to date than me. But it is going to be something like £500/m of perimeter and a huge amount of mess.

Why does it need underpinning?

[Conor]

Realistically, you've two options if you want a warm house. 100mm EWI directly on to the existing walls. Don't worry about the 'dash. Second, is the knock and rebuild. Any talk about widening cavities etc is crazy.

 

We were in a very similar position, but with even less work than you are describing. Rebuilding on the same footprint worked out more cost effective once you calculate long term running costs and resale.

[Russell griffiths]

3 hours ago, saveasteading said:

Somebody will be more up to date than me. But it is going to be something like £500/m of perimeter and a huge amount of mess.

Why does it need underpinning?

£1000 per lin metre at the moment I’m led to believe talking to local lads. 

[Russell griffiths]

What’s the thoughts on Ewi on a cavity wall then. 
 

I was under the impression that a cold uninsulated cavity would still be cold no matter what thickness of Ewi is added. 
so with a cold cavity then isn’t the inner skin still cold. 
 

I thought IWI was the go to with a cavity. 

[saveasteading]

34 minutes ago, Russell griffiths said:

cold no matter what thickness of Ewi is added. 

If it helps anyone, here is the Woozle principle that can be applied to almost any Mechanical Physics.

In this case it is a heat Woozle. (WZe?)

 

Imagine a warmed up Woozle in your living room. To me they look like a yellow emoji figure with 2 arms and 2 legs.

It is trying to escape out to the cold, wriggling through microscopic gaps in your wall.  

Thus any resistance works whether inside or outside or in-between. 

Area of less resistance ( whether universal or local) allow easier escape.

There are other factors eg condensation but that is a slightly different analogy. 😳 I can't find one with limbs.

 

Some day I will introduce the pulling and pushing ones that make beams work.

 

It isn't my theory. My wife was taught about Woozles at Uni by a prof who could communicate, and she told me. Often used by me.

[lookseehear]

I thought you could only ewi a cavity wall if the cavity was either filled (eg with EPS beads) or sealed, otherwise you end up with a well insulated outer leaf and a cold cavity.

[Iceverge]

On 20/12/2024 at 17:45, allthatpebbledash said:

 

 

On 20/12/2024 at 17:45, allthatpebbledash said:

What’s the sunk cost fallacy? 

 

Where the cost and time of past efforts make it mentally impossible to change course. 

 

 

 

[saveasteading]

1 hour ago, lookseehear said:

you end up with a well insulated outer leaf and a cold cavity.

I forgot to end my post with this. Insulation anywhere will reduce heat transfer. You could put some inside and some outside and less heat will escape. If it's outside then the cavity will get less cold. But bricks have resistance and so does enclosed  air, so it all adds up.

[ProDave]

50 minutes ago, saveasteading said:

I forgot to end my post with this. Insulation anywhere will reduce heat transfer. You could put some inside and some outside and less heat will escape. If it's outside then the cavity will get less cold. But bricks have resistance and so does enclosed  air, so it all adds up.

I think the concern with a non insulated cavity is you might be heading for the plasterboard tent principle with a cold cavity, likely vented to the loft negating much of the benefit of EWI.  Surely if you are adding EWI to an unfilled cavity you should at a very minimum ensure the entire top of the cavity is closed off so cold air from the loft cannot enter, and any warmth created in the cavity from the house cannot escape.

[saveasteading]

23 minutes ago, ProDave said:

Surely if you are adding EWI to an unfilled cavity 

Agreed there are other considerations, including vapour. 

The geometry is often overlooked too, with any extra thickness clashing with the eaves or requiring a gable oversail.

It's one of these questions where we don't know enough, and expert professional advice should be taken.

[Iceverge]

1 hour ago, saveasteading said:

including vapour.

 

Vapour.....

 

 

It's like worrying about fog when rain is the issue. 

 

Airborne moisture carried by leaks through poor airtighness is the elephant in the room. 

 

 

[joe90]

2 hours ago, saveasteading said:

I forgot to end my post with this. Insulation anywhere will reduce heat transfer. You could put some inside and some outside and less heat will escape. If it's outside then the cavity will get less cold. But bricks have resistance and so does enclosed  air, so it all adds up.

If your going to all this trouble then why not fill the cavity with beads and have even more insulation?