Hello from someone considering demolishing and rebuilding

[Norbert]

We are considering the drastic step of demolishing and rebuilding our house where we have lived for 40 years. This is because in winter it is cold, damp and draughty, but it is not worth spending a lot of money to address these issues as it is also subject to flooding. The house is on a wonderful plot with great views. There seems to be absolutly no possibility of getting any equivavent plot in the area. The outline plan is to build a timber frame house, possibly to passivhus standard on a new 2 meters block wall on the same footprint. Thus it would be a 2 floor house with a full height cellar that is designed to take flood water in and drain away without damage.

 

We are at the start of the project and have just appointed architects. I consider myself to be a competant DIYer having done a lot to this house, and another one over the years, with experience of most trades. My emotions vary from being excited by the prospect, to being terrified. At present I am spending a lot of time investigating aspects of technology, fittings, techniques etc. trying to get myself in a position where we can make sensible decisions when the time comes. I anticipate that I may be posting for help and ideas on a wide variety of topics as the project progresses.

 

Edited June 7, 2023 by Norbert

[Susie]

Welcome to forum lots of helpful ideas on here from other self builders. 

[Big Jimbo]

Good Morning. Do it. You will have a fantastic place to live for the rest of your life, and much smaller bills.

[Mr Punter]

If it is a large plot, is there any possibility that you could alter the topography by building up levels?  If you have a large excavator and dumper you can make a huge difference.  I would not bother with a cellar on the flood plain. You will fill it with stuff and if there is a flood warning you will supposedly have to shift it all upstairs.

[Bozza]

Welcome.  Have you done your research with building control, insurers, mortgage lenders etc with regard to the flooding risk.  I’d imagine that could be a big issue.
 

i seem to recall a Grand Designs house a few years ago whereby when flooded the house would float upwards.  And the Dutch live in houses, so there will definitely be plenty of technical solutions.  

is it concealable to build a house on some sort of legs or frame that could double as a car port?

 

passive-house standard is important to some some self builders but not essential to get a very well insulated and efficient house.

 

your project sounds very challenging and interesting.  Good luck ! 
 

 

[Dave Jones]

wouldn't have thought an expensive timber frame in a flood area was a good idea.

 

One of the expensive concrete lego block systems would be idea though as you could bump the height really easily and it would be waterproof soon as the concrete sets.

 

Just be careful of the dealers as they have a habit off going bust with your money.

[Nickfromwales]

15 hours ago, Dave Jones said:

wouldn't have thought an expensive timber frame in a flood area was a good idea.

 

One of the expensive concrete lego block systems would be idea though as you could bump the height really easily and it would be waterproof soon as the concrete sets.

 

Just be careful of the dealers as they have a habit off going bust with your money.

🤦‍♂️

If elevated above the known (historic information) flood levels, then anything can be built as it will never see flood waster. Neither has to be "expensive".

 

EPS - based ICF would seem to fit the bill, but vermin protection would be an issue, so would fire-proofing the EPS. Block undercarriage would defo be the best option here, as the flood defence/ platform, then build whatever you like on top  

[Dave Jones]

8 hours ago, Nickfromwales said:

🤦‍♂️

If elevated above the known (historic information) flood levels, then anything can be built as it will never see flood waster. Neither has to be "expensive".

 

EPS - based ICF would seem to fit the bill, but vermin protection would be an issue, so would fire-proofing the EPS. Block undercarriage would defo be the best option here, as the flood defence/ platform, then build whatever you like on top  

 

expensive as either method are getting on for double the cost of a traditional build just to be clear.

[Thorfun]

On 07/06/2023 at 09:16, Big Jimbo said:

Good Morning. Do it. You will have a fantastic place to live for the rest of your life, and much smaller bills.

+1

[Nickfromwales]

6 hours ago, Dave Jones said:

 

expensive as either method are getting on for double the cost of a traditional build just to be clear.

Time is expensive, and has a specific value to the right self builder. 
Quick build = less rental costs. 

[Dave Jones]

1 hour ago, Nickfromwales said:

Time is expensive, and has a specific value to the right self builder. 
Quick build = less rental costs. 

 

yep as ive said before, if you have a 12 week build to move in then paying double may be worth it. not many operate on that window though do they so its pissing cash away for no reason.

[Thorfun]

5 minutes ago, Dave Jones said:

 

yep as ive said before, if you have a 12 week build to move in then paying double may be worth it. not many operate on that window though do they so its pissing cash away for no reason.

sustainability? reduced carbon footprint? speed to watertight? environmental impact? lower as built tolerance levels?

Edited June 9, 2023 by Thorfun

[Dave Jones]

15 hours ago, Thorfun said:

sustainability? reduced carbon footprint? speed to watertight? environmental impact? lower as built tolerance levels?

 

yep lots of reasons to try and justify burning the extra cash for little if any benefit.

 

All personal preference at the end of the day.

[Norbert]

On 07/06/2023 at 11:17, Mr Punter said:

If it is a large plot, is there any possibility that you could alter the topography by building up levels?  If you have a large excavator and dumper you can make a huge difference.  I would not bother with a cellar on the flood plain. You will fill it with stuff and if there is a flood warning you will supposedly have to shift it all upstairs.

Yes it is a largish plot, but I cannot see any advantage in building up levels, other than my plan of raising the whole house by 2 meters on block walls. That inevitably creates a cellar, well unless it is just filled with rubble, but I cannot see any advantage to that. It would make no difference to what goes on top. Also I can see the cellar being useful, bit of a man cave and it would be easy enough to keep things above any likely flood level

[Norbert]

On 07/06/2023 at 11:53, Bozza said:

Welcome.  Have you done your research with building control, insurers, mortgage lenders etc with regard to the flooding risk.  I’d imagine that could be a big issue.

No, not yet. All to be done as part of getting planning permission. Regards insurers I am living there now and have insurance. I would think they would be delighted to have their risk reduced by raising the house 2 meters!

[Norbert]

On 07/06/2023 at 11:53, Bozza said:

is it concealable to build a house on some sort of legs or frame that could double as a car port?

That is in effect what I am thinking of doing, but not a car port, more a man cave, patio, garden room etc.

[Norbert]

On 09/06/2023 at 00:13, Nickfromwales said:

If elevated above the known (historic information) flood levels, then anything can be built as it will never see flood waster. Neither has to be "expensive".

 

EPS - based ICF would seem to fit the bill, but vermin protection would be an issue, so would fire-proofing the EPS. Block undercarriage would defo be the best option here, as the flood defence/ platform, then build whatever you like on top

Exactly. Plus I cannot see the advantage of ICF as this whole level will be outside the thermal envelope. Some kind of vermin mesh needed between block base and TF.

[Nickfromwales]

On 11/06/2023 at 11:57, Norbert said:

Plus I cannot see the advantage of ICF

That was because it would give you a lower structure that was nearly 100% non-hygroscopic. If a flash flood actually took water levels up to the house, the EPS ICF would be unaffected. A TF would have to be cut open to evacuate lost insulation / clear crud out of cavities etc, whereas with EPS ICF you'd only be replacing the bottom of the plaster boards. 

[scottishjohn]

where are you going to live while this is going on?

that could be alot of money -with inevitable hold ups -that will happen 

have you thought about digging a new found around exsitiing house and do you ICFwalls  while house is still livable -then demolish it inside --could save you lots in money and you can do it at your own pace then ?

[Norbert]

19 hours ago, Nickfromwales said:

hat was because it would give you a lower structure that was nearly 100% non-hygroscopic. If a flash flood actually took water levels up to the house, the EPS ICF would be unaffected. A TF would have to be cut open to evacuate lost insulation / clear crud out of cavities etc, whereas with EPS ICF you'd only be replacing the bottom of the plaster boards. 

But what would be the problems with the block walls taking up some moisture in the event of a flood? The water would drain away and they would dry naturally over time. In the last flood 13 years ago all the gypsum plaster was removed,the brick, block and stone walls remained, allowed to dry then replastered. This time no gypsum or electrics down there, just blocks so should be naturally flood resiliant as far as I can see.

 

I agree that if a future flood rose to 1.85 meters above the highest historic level so far and reached the TF structure that would indeed be a problem. However having lived on the site by the river for 40 years. and knowing the catchment very well, and the lie of the local land, I think that is very unlikely. However I will be comissioning a flood risk survey to get an official max possible flood level. That will be needed for planning permission. However the height of the TF house will be above other local houses that I not considered to be at flood risk. If we need to take the block walls higher than 2 meters to be sure then we can do that I guess.

Edited June 13, 2023 by Norbert

[Nickfromwales]

20 minutes ago, Norbert said:

I agree that if a future flood rose to 1.85 meters above the highest historic level so far and reached the TF structure that would indeed be a problem. However having lived on the site by the river for 40 years. and knowing the catchment very well, and the lie of the local land, I think that is very unlikely. However I will be commissioning a flood risk survey to get an official max possible flood level. That will be needed for planning permission. However the height of the TF house will be above other local houses that I not considered to be at flood risk. If we need to take the block walls higher than 2 meters to be sure then we can do that I guess.

Sounds sensible, all good! The flood risk survey will likely be required for insurances also, so 2 birds with 1 stone there.

[Iceverge]

On 11/06/2023 at 11:47, Norbert said:

Yes it is a largish plot

 

Can you build another house beside you current one on the plot and then knock the existing one down when you are finished, at least you'll have somewhere to live in the interim. 

 

Personally I would bin any idea of a basement/cellar. It'll just be a liability when the flood does come. Poured concrete walls would be my preference for anything below ground regarding flooding too. Be cautious cutting it too fine with any proposed flood levels, we're all aware of the higher incidence of extreme weather events 

[jayc89]

I live in a flood risk zone 2 area, it's never flooded, never will, barring some dykes, the nearest water source is some 7 miles away, yet local guidelines point blank refuse any new developments with cellars etc. Shame really as I'd have liked a bit of a man cave in the extension. 

If I was doing one, I'd be using ICF below ground. 

[Norbert]

4 hours ago, Iceverge said:

Personally I would bin any idea of a basement/cellar.

So if I demolish and rebuild on the same footprint 2 meters higher what do you suggest that I do with the volume (footprint area x 2 mtrs) that will inevitably be created?

[Iceverge]

9 hours ago, Norbert said:

So if I demolish and rebuild on the same footprint 2 meters higher what do you suggest that I do with the volume (footprint area x 2 mtrs) that will inevitably be created?

 

I would investigate building a replacement house adjacent to the house. It'll save loads of cash during the build and really take the time pressure off. 

 

On the subject of a void you could just fill it in.  Otherwise consider it for something that was either easily removed during floods or preferably something that was not troubled by them. 

 

A car port or a few rainwater tanks maybe. 

 

On a large plot however, why compromise? Just build what you need above flood level and fill in below. Leave the burrowing to the hobbits.