Renovation and Extension = money pit

[Roger440]

7 hours ago, Clark Kent said:

 

 

@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?

 

You havent actually told us the wall make up and if you have a DPC etc. This will dictate what you do with regard IWI.

 

But, yes, you do risk interstatial condensation if its not done right.

 

But need to know wall make up.

 

Yes, to the cold bridge. Not much you can do about that unless you insulate those too!

[Clark Kent]

The wall construction is brick-cavity-brick. The cavity has been retro filled in the past with what appears to be blown mineral wool fibres, there is also a DPC.

 

I don’t really fancy cladding internal walls as well.

[Roger440]

21 hours ago, Clark Kent said:

The wall construction is brick-cavity-brick. The cavity has been retro filled in the past with what appears to be blown mineral wool fibres, there is also a DPC.

 

I don’t really fancy cladding internal walls as well.

 

Well that keeps things pretty straight forward.

 

No need to bugger around with lime based breathable products.

 

Can you not clean out the cavity and refill with beads?

 

Then add some PIR internally. Will need a decent vapour barrier though. Like many on here, punch some details into this and see at what point interstatialm condensation occures. https://www.ubakus.de/en/r-value-calculator/index.php?

 

[Iceverge]

On 22/12/2023 at 14:12, Ferdinand said:

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 have a post on this somewhere. I'll try to find it. From what I remember it's not as good as digging up the floor but it certainly helps. 

 

 

[Iceverge]

 

Thats it. 

[Clark Kent]

8 hours ago, Iceverge said:

 

 

Thats it. 

 

Thanks for linking, I’ll have a good read….

[Redbeard]

On 22/12/2023 at 13:49, Clark Kent said:

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

Yes, but you mitigate that by returning onto the relevant wall (internal or party). Typical return is min 400mm-ish

[Adsibob]

@Clark Kent are you fitting MVHR and making the house fully airtight? If so, this may help keep your bills down. We extended and renovated a 1930s semi, and although we did add EWI to the walls and 100mm of PIr under the floors , it is not anywhere near passiv standard, yet I’m convinced the MVHR saves us quite a bit of money, because we don’t need to run our UFH very long to warm up the house. Even in the depths of winter it’s only on 4-5h a day on ground floor and 2.5hr a day in kids bedroom. When I’m working for the day in my study I maybe switch it on in that room for half the day. Occasionally switch it on in the bathrooms, but they are all on the upper floors of the house so get indirect heat anyway from downstairs.

Edited December 24, 2023 by Adsibob

[Clark Kent]

3 hours ago, Redbeard said:

Yes, but you mitigate that by returning onto the relevant wall (internal or party). Typical return is min 400mm-ish

 

How do you lose the thickness of the IWI after 400mm?

 

1 hour ago, Adsibob said:

@Clark Kent are you fitting MVHR and making the house fully airtight? If so, this may help keep your bills down. We extended and renovated a 1930s semi, and although we did add EWI to the walls and 100mm of PIr under the floors , it is not anywhere near passiv standard, yet I’m convinced the MVHR saves us quite a bit of money, because we don’t need to run our UFH very long to warm up the house. Even in the depths of winter it’s only on 4-5h a day on ground floor and 2.5hr a day in kids bedroom. When I’m working for the day in my study I maybe switch it on in that room for half the day. Occasionally switch it on in the bathrooms, but they are all on the upper floors of the house so get indirect heat anyway from downstairs.

 

MHVR is something I have looked at and would really like to do but currently the budget wouldn’t stretch that far. 

[SteamyTea]

On 24/12/2023 at 20:33, Clark Kent said:

MHVR is something I have looked at and would really like to do but currently the budget wouldn’t stretch that far. 

Will the budget go as far as fitting the pipework and vents?

Can fit cheap inline fans then. Or make your own MVHR.

[Onoff]

1 hour ago, SteamyTea said:

Or make your own MVHR.

 

When are you making your MK3 version?

 

There's always this:

 

https://www.builditsolar.com/Experimental/DIYHRV/DIYHRV.htm

[SteamyTea]

1 hour ago, Onoff said:

When are you making your MK3 version?

 

Shall start tomorrow, all I need is a trip out in an old, renovated, Capri to give me inspiration.

[Onoff]

3 minutes ago, SteamyTea said:

Shall start tomorrow, all I need is a trip out in an old, renovated, Capri to give me inspiration.

 

That's actually rather good, very hurtful but good...

 

😂

[SteamyTea]

1 minute ago, Onoff said:

 

That's actually rather good, very hurtful but good...

 

😂

I need a couple of car radiators.

Then we can get on with both projects drekly.

 

[Clark Kent]

17 hours ago, SteamyTea said:

Will the budget go as far as fitting the pipework and vents?

Can fit cheap inline fans then. Or make your own MVHR.

 

Yes it probably would, that’s something I shall do as I’d like to go down that route in the future maybe.

[Clark Kent]

On 25/10/2021 at 01:11, Iceverge said:

Finally I've done all I can to avoid digging the floor, Externally insulated with 250mm EPS 700mm below the ground. Included a 1m wing and added 25mm of EPS above the floor to take the underfloor heating pipes. U value is 0.27 overall. I'm going to make a crude estimation and say this is the equivalent of putting 250mm EPS in your floor and not taking any measures against the wall/floor junction. 

 

 

 

 

 

The lesson of all this is 2 fold, firstly if you can't or really don't want to dig up your floor there are other options.

Secondly insulation is of limited use without getting a handle on thermal bridges. 

 

 

 

 

 

@Iceverge Cheers for the link, was most interesting. Discussed it with my builder and he was less convinced, he’s also adamant that a heat pump is the wrong way to go though.

 

[Iceverge]

50 minutes ago, Clark Kent said:

 

 

@Iceverge Cheers for the link, was most interesting. Discussed it with my builder and he was less convinced, he’s also adamant that a heat pump is the wrong way to go though.

 

 

I'm sure your builder is a good sort but

they're very cautious by nature and will be slow to change from a method they understand. 

 

Put in the biggest radiators you can fit and forget UFH is my advice unless you're prepared to dig out the floor and put in 300mm EPS. A correctly sized ASHP work best with as low a flow temp as possible. To be able to extract the heat most efficiently from that flow you need the most emitter power. This means a shallow screed with closely spaced pipes or big radiators. 

 

Do you have any sketches of the extension (unidentified for a public forum of course) ?

 

 

 

 

 

 

Edited January 2 by Iceverge

[Clark Kent]

I have some drawings, still a work in progress whilst I try to iron out details/decide which way to go…

 

I have known the builder since uni so he’s a very old friend. Which is why I’m not just dismissing his pessimism out of hand, had lots of people warn me off of ASHP but none ever had any real world experience….one even went on to have one fitted himself, by his plumber whom I’m sure probably over-specced as they generally do with a combi

 

[ETC]

Have you made a BC application?

Wall panels need restraint and openings look too big for the wall panels.

[Clark Kent]

No not yet, these drawings were submitted to the SIP supplier and they produce all the relevant building control drawings.

[Iceverge]

On 02/01/2024 at 06:37, Clark Kent said:

I have some drawings, still a work in progress whilst I try to iron out details/decide which way to go…

 

I have known the builder since uni so he’s a very old friend. Which is why I’m not just dismissing his pessimism out of hand, had lots of people warn me off of ASHP but none ever had any real world experience….one even went on to have one fitted himself, by his plumber whom I’m sure probably over-specced as they generally do with a combi

 

 

That design looks fine, without accurate dimensions its a tad hard to judge but it's good really. 

 

However, (stroking my passive house chin) there's thermal bridges galore. 

 

I would love to suggest wrapping the whole house, including the new bit in 200mm Rockwool EWI but I have a feeling some Draconian conservation law will prevent that. 

 

I also think living there whilst building is ongoing will be impossible. 

 

[Clark Kent]

@Iceverge thanks for the feedback. I’d be most interested in hearing solutions to the thermal bridge problems, or even just explain to me where they are (I’m assuming the junction between existing wall and SIPs panel for a start).

 

I’m not gong for passive standards…probably nowhere near tbh. But, I would like to make it as efficient as possible and potentially get the bills down (or just stop them going up!)

 

The detailing and extra work I’m doing on the drawings will hopefully mitigate some of these problems. Maybe the SIP supplier will advise? Although I rather suspect they will be more interested in banging it out as quick as possible.

 

As for wrapping the whole house…I’d consider it but the local authority wouldn’t. It was an ache in the balls getting permission for the extensions let alone changing the appearance of the house.

[Iceverge]

@Clark Kent Sorry for the delay.  Assuming you will suck out the mineral wool in the cavity and replace with foam or GPS beads. 

 

I've drawn some of the lightly escape routes for heat. The house will most lightly have brick closed cavities at the window jambs. When adding a cavity wall extension it's difficult to deal with joining to the existing building and you'll have a heat leak here too. That's why in an ideal world a complete wrap around blanket of insulation would be nice. You could deal with most of these by adding an internal insulation layer too but it'll rob a lot of space from the house. 

 

 

 

[Onoff]

You can make a nod towards cold bridging by internally, airtight taping &  insulating at the window reveals. I used 27mm insulated plasterboard. 

 

 

 

 

 

 

 

 

My windows aren't in the best place, being level with the outside skin. 

[Clark Kent]

Thank you for the feedback @Onoff & @Iceverge, I’ve done a bit of research and am thinking of using insulated plasterboard to negate the cold bridge from the existing external wall into the new extension (Blue line on plan).

 

Also regarding the existing house, when replacing the windows I was going to add cavity closers and insulated plasterboard for the internal reveals as per @Onoff suggested.

 

I’m also thinking I need to do something on the ground floor where the rear extension interfaces the existing building.

 

I’m not a huge fan of the standard detail supplied by the SIPs company for interfacing/connecting to an existing wall. It’s just a timber baton/sole plate with a DPM that the sip panel is screwed to. It’s an obviously a cold bridge. Although I guess it’s not in their remit to detail this kind of thing out.