Renovation and Extension = money pit

[Clark Kent]

Hello

 

Been lurking on this site for some time trying to glean information and thought it about time to join in and introduce myself….

 

We bought our house about 18 months ago in a small village in Kent, it was in poor condition as the lady that owned it previously was a bit of a hoarder and had let it go…but we could see the potential.

 

I’m a keen DIYer, fairly practical so intend on doing a large amount of the work myself, or at least overseeing (project managing as they like to say on Grand Designs).

 

The house has been gutted (mainly to get rid of the smell!) and made liveable to a certain extent, currently our only heat supply is a log burner and some oil filled electric rads that we use if we’re feeling really bougie.

 

The Plan is-

 

Double storey side and single storey rear extension

Upgrading existing insulation

Replace windows

ASHP (maybe)

 

I’d like to make the old part as thermally efficient as possible, obviously financial and complexity will dictate how far I can take this.

 

I’ll have plenty of questions, be kind though as I’m a relative newb to these things and nobody was born with the knowledge

 

[Onoff]

10 minutes ago, Clark Kent said:

previously was a bit of a hoarder and had let it go

 

Sounds like my place (in Kent).

 

[Roger440]

18 minutes ago, Clark Kent said:

Hello

 

Been lurking on this site for some time trying to glean information and thought it about time to join in and introduce myself….

 

We bought our house about 18 months ago in a small village in Kent, it was in poor condition as the lady that owned it previously was a bit of a hoarder and had let it go…but we could see the potential.

 

I’m a keen DIYer, fairly practical so intend on doing a large amount of the work myself, or at least overseeing (project managing as they like to say on Grand Designs).

 

The house has been gutted (mainly to get rid of the smell!) and made liveable to a certain extent, currently our only heat supply is a log burner and some oil filled electric rads that we use if we’re feeling really bougie.

 

The Plan is-

 

Double storey side and single storey rear extension

Upgrading existing insulation

Replace windows

ASHP (maybe)

 

I’d like to make the old part as thermally efficient as possible, obviously financial and complexity will dictate how far I can take this.

 

I’ll have plenty of questions, be kind though as I’m a relative newb to these things and nobody was born with the knowledge

 

 

Lots an lots of good info on here. Should keep you occupied for many many hours.

 

[Clark Kent]

@Onoff maybe it’s a Kent thing….the smell was gopping though.

 

@Roger440 yes, I’ve whittled many an hour away on this forum already 👍🏻

 

I think the main thing I’m interested in atm is insulating my existing slab, as far as I have read the biggest heat loss seems to be from the edges. I will only have the one (existing) side exposed due to the side and rear extension so I’m hoping this makes the situation a lot better.

 

Digging it out and replacing isn’t really viable.

[Iceverge]

57 minutes ago, Clark Kent said:

I’d like to make the old part as thermally efficient as possible, obviously financial and complexity will dictate how far I can take this.

 

Can you raise funds for a complete rebuild? 

 

Doesn't have to be grand designs (infact it's better if it's not) 

[Clark Kent]

45 minutes ago, Iceverge said:

 

Can you raise funds for a complete rebuild? 

 

Doesn't have to be grand designs (infact it's better if it's not) 

I don’t think that a complete rebuild would be feasible as it’s a semi (sorry forgot to mention that) and we’re in an AONB so gaining planning for anything is a pain

[Onoff]

Even with a 100mm concrete slab atop a 300mm eps raft, a previous member calculated 8% of his heat loss was through the floor.

 

@oranjeboom here did a complete dig out on an existing build.

[Onoff]

Just now, Clark Kent said:

we’re in an AONB

 

It's great isn't it. Next you'll tell me you're under Sevenoaks!

[Clark Kent]

It’s funny as when i first started looking into heat pumps and UFH the vendors were all telling me that the least heat is lost through the floor “heat rises-right!”

 

Luckily I’m a tad cynical and started trying to dig down into these claims a bit.

 

5 minutes ago, Onoff said:

Even with a 100mm concrete slab atop a 300mm eps raft, a previous member calculated 8% of his heat loss was through the floor.

 

@oranjeboom here did a complete dig out on an existing build.

 

I did see this, ideally I would do but tbh financially and the fact that we’re living in the property I can’t see it being a flyer…I’ve considered many scenarios such as sending the family on holiday and doing the work but realistically I don’t think it’d work.

[JohnMo]

17 minutes ago, Clark Kent said:

heat is lost through the floor “heat rises-right!”

Obviously not looking much further than their nose end. Convection, conduction, and radiation are principal mechanisms for heat transfer, all are in play within a house.

 

Conduction is the transfer of heat by two objects that are in direct contact with one another. It occurs when in contact with a cold or warm object. For example, your floor will try to conduct to the cold ground below it

 

Convection is the transfer of heat to the air surrounding an object. The warmed air rises away and is replaced by cooler air that is subsequently heated. This is the only thing your supplier wanted to talk about.

 

Radiation is the transfer of heat via infrared waves. This occurs between any two objects when their temperatures differ. A radiator can warm a room via radiant heat. On a sunny day, the radiation from the sun warms the skin.

[Clark Kent]

6 minutes ago, JohnMo said:

Obviously not looking much further than their nose end.

 

I think more of the case of not looking further than their order books….

[Onoff]

45 minutes ago, Clark Kent said:

It’s funny as when i first started looking into heat pumps and UFH the vendors were all telling me that the least heat is lost through the floor “heat rises-right!”

 

Luckily I’m a tad cynical and started trying to dig down into these claims a bit.

 

 

I did see this, ideally I would do but tbh financially and the fact that we’re living in the property I can’t see it being a flyer…I’ve considered many scenarios such as sending the family on holiday and doing the work but realistically I don’t think it’d work.

 

The "one room at a time" approach would work for me. The ground floor is big enough that we could have a temporary lounge whilst we do the lounge / diner. Even though you'd have to traverse that area by scaffold boards (for months 😂 ) whilst I gutted it and dug down / built it back up.

 

Key to mine is digging up the central "stairs room", insulating underneath and placing the UFH manifold there. Thereafter rooms could be done one at time. I've the space even for a temporary kitchen whilst I do that. I have a plan but SWMBO thinks I'd take too long. Meanwhile we're getting older in the plasterboard tent.

[Iceverge]

Build the extension first. Isolated from the old bit as much as possible. New power, water etc direct in there. Keep all your new wet rooms and kitchen there. 

 

Then move in there and renovate the old bit afterwards into bedrooms, offices and living rooms. 

 

Then knock through and join them up. 

 

 

[Roger440]

7 hours ago, Clark Kent said:

It’s funny as when i first started looking into heat pumps and UFH the vendors were all telling me that the least heat is lost through the floor “heat rises-right!”

 

Luckily I’m a tad cynical and started trying to dig down into these claims a bit.

 

 

I did see this, ideally I would do but tbh financially and the fact that we’re living in the property I can’t see it being a flyer…I’ve considered many scenarios such as sending the family on holiday and doing the work but realistically I don’t think it’d work.

 

Having done this at my last place, ive priced up doing it here. Even with me doing the bulk of the work, id be looking at best part of £5K to dig out, insulate anmd reinstate concrete.

 

£5k buys you an awful lot of energy loss.

 

If you have space, fit an overlay system, if not, just cut grooves in exsisting for the UFH. These guys will rent you the tool: https://www.boels.com/en-gb/hire/underfloor-heating-chaser-230-v/p/35221

[Clark Kent]

@Roger440 I have considered an overlay system. I also had a quote from a firm regarding cutting the underfloor into the existing concrete floor after coming across them at Build it Live. I’ve discounted this option as I think the heat would literally be sucked out of the room into the ground.

 

I don’t know the existing slab build up but I’m assuming it’s concrete slab directly onto aggregate or mud.

 

I’m thinking that due to the worst case of heat loss through the floor perimeter being counteracted by the new well insulated slabs on two sides I might be able to run a 25mm-50mm PIR board over the ground floor under an overlay system.

 

I’ve also read on here 100mm PIR is minimum below underfloor, but then there’s also a post stating that if you were pouring a slab the size of a warehouse there’s no need to insulate the centre as heat loss is minimal. The majority of heat is lost through the floor edges.

 

It’s difficult to know what to do, the salesman will tell you that heat loss is minimal through the floor. A builder friend has laid lots of overlay systems and found them to be very good.

 

I’m sure they work and will keep the house warm but the million dollar question is how much will it cost to run….

 

I guess the other thing to mention is that we aren’t on mains gas here, so it’s either LPG or electricity. I like the idea of the renewables route but again, I only have a finite budget.

[joe90]

As you say budget is the key thing here (unlike grand designs mostly)and you need to max that out in insulation, saying that the first inch of insulation gives the biggest payback (diminishing returns principle) so perhaps IWI linked to overfloor insulation and a floating floor over would be a good start 🤷‍♂️.

[de devil tail]

It certainly sounds like a tough call on ways to proceed.

Getting a good thermal envelope will be key.

[Roger440]

3 hours ago, Clark Kent said:

@Roger440 I have considered an overlay system. I also had a quote from a firm regarding cutting the underfloor into the existing concrete floor after coming across them at Build it Live. I’ve discounted this option as I think the heat would literally be sucked out of the room into the ground.

 

I don’t know the existing slab build up but I’m assuming it’s concrete slab directly onto aggregate or mud.

 

I’m thinking that due to the worst case of heat loss through the floor perimeter being counteracted by the new well insulated slabs on two sides I might be able to run a 25mm-50mm PIR board over the ground floor under an overlay system.

 

I’ve also read on here 100mm PIR is minimum below underfloor, but then there’s also a post stating that if you were pouring a slab the size of a warehouse there’s no need to insulate the centre as heat loss is minimal. The majority of heat is lost through the floor edges.

 

It’s difficult to know what to do, the salesman will tell you that heat loss is minimal through the floor. A builder friend has laid lots of overlay systems and found them to be very good.

 

I’m sure they work and will keep the house warm but the million dollar question is how much will it cost to run….

 

I guess the other thing to mention is that we aren’t on mains gas here, so it’s either LPG or electricity. I like the idea of the renewables route but again, I only have a finite budget.

 

An overlay system will be way better than cutting grooves into the floor.

 

But you do then need to deal with all the knock on consequences of that, odd depth fist step on the stairs being the one i really dont like.

 

Im faced with the exact same choice. Other consequences in my case, include having to replace or re-locate the rear door, as whilst its a new decent insulated door, its so close to the floor, we cant even have a doormat. Easy answer, raise it. Not so easy as the joists for the flat roof are directly above. So either a new door or a lot of buggering about. Which is all cost.

 

Im minded to cut grooves in the exsisting, perfectly good slab. Given the front half is a 150 year old stone cottage with no DPC, a bit of sideways heat loss into the wall is probably no bad thing. As i said earlier, its going to be £5k minium to replace the floor. So 16700 kwh of energy at current prices. Likely life expectancy of me, 25 years.

 

You could if you were feeling keen, (i nearly did this at the last place) cut a sliver of the slab all the way round and replace with insulation. Would be difficult, time consuming and messy, but would cost bugger all if you did it yourself.

[Clark Kent]

19 minutes ago, Roger440 said:

 

But you do then need to deal with all the knock on consequences of that, odd depth fist step on the stairs being the one i really dont like.

 

 

Yes I’ve tried to weigh all this up. The stairs are pretty knackered anyway so I’m of a mind to replace completely as I believe that differing height risers may fall foul of building regs, if they looked that closely although I don’t think they will.

 

We’re taking the entire rear wall out for the extension and relocating the front door so that problem is dealt with. I can change the height of the other existing internal doors myself.

 

@joe90 I’m not great with all the acronyms on here, I’m guessing IWI is internal wall insulation though? I was indeed also considering some internal insulation. Need to read a bit more about it though as the little I have read suggests it could cause condensation.

 

I know I could use a natural breathable product but that would necessitate using lime plaster and breathable paints etc, sounds like a PITA. Finding a plasterer that would do it could be difficult and costly.

 

If I were to use IWI on the exterior elevations would any internal walls coming off of that exterior wall become a cold bridge?

[Ferdinand]

On 21/12/2023 at 12:35, Onoff said:

Even with a 100mm concrete slab atop a 300mm eps raft, a previous member calculated 8% of his heat loss was through the floor.

 

@oranjeboom here did a complete dig out on an existing build.

 

Not sure that is quite correct -wasn't it Jeremy and that when he installed ufh on top of a 300mm eps raft that 8% of the ufh heat went downwards, not of all his heat lost from the house.

 

Perhaps me putting too much on precise wording.

 

[joe90]

17 minutes ago, Clark Kent said:

I’m guessing IWI is internal wall insulation though? I was indeed also considering some internal insulation. Need to read a bit more about it though as the little I have read suggests it could cause condensation.

Yes, just ask the question here (start a new thread or search for or search for previous threads about the best way to do it and lots of practical advise will be forthcoming. All this work starts with you knowing your budget.

[Ferdinand]

@Clark Kent

 

Have you considered what is called "skirt insulation" - where you dig a trench round the outside and make it a French Drain * with 300mm (say) of insulation up against the outside of your house to a depth of (say) 600 or 900mm?

 

The mechanism is that the soil temperature at that depth is pretty stable, and the ground under your house heats up over time because the thermal path away is now much longer. Having a warm ground reduces your heat loss downwards.

 

You lose less on the neighbour side because their house extends around your boundary to them, heating up the ground there.

 

Contraindications for this may be eg that there is a high water table, and water movement may steal your heat - which is what the French Drains can be there to divert to keep your patch dry.

 

* French Drains are at their simplest gravel filled trenches with the gravel wrapped up in weed membrane. Easy to do if you need. I put a loose laid path of heavy slabs on top - you get a free hidden route to run pipes and cables.

[Clark Kent]

13 minutes ago, Ferdinand said:

@Clark Kent

 

Have you considered what is called "skirt insulation" - where you dig a trench round the outside and make it a French Drain * with 300mm (say) of insulation up against the outside of your house to a depth of (say) 600 or 900mm?

 

 

I like this idea….definitely more viable than taking the whole floor slab out 

[Mr Punter]

Perhaps don't bother with UFH.  Cover the slab with, say, 40mm PIR type insulation and top with 22mm chipboard plus your choice of floor finish.  You will lose 60mm headroom.  You can either have radiators or heated skirtings.  For a heat source, you may find that oil is cheapest per kWh.  If you oversize the rads and plan ahead you could swap out for a heat pump in the future.

 

If / when you ditch the staircase, look at whether the replacement can be located to make better use of your space.  It is often quite easy to cut out and trim a timber joisted floor.

[Onoff]

2 hours ago, Ferdinand said:

 

Not sure that is quite correct -wasn't it Jeremy and that when he installed ufh on top of a 300mm eps raft that 8% of the ufh heat went downwards, not of all his heat lost from the house.

 

Perhaps me putting too much on precise wording.

 

 

Not sure, found this: