Hello from Devon and floor insulation question

[sam]

I introduced myself back in the ebuild days but I've mostly been lurking here since... thanks for all the interesting posts which I have enjoyed reading. For many years it was our intention to self build but failure to obtain planning permission (long shot) and failure to find another suitable plot meant we have settled for a renovation project instead. We dreamed of getting close to passive house standard on a new build.

 

We have been living in our 1950s house in East Devon for a few months now and are trying to make decisions on what to do. Having read so many interesting response to people's queries I'm looking forward to asking a few questions.

 

The highest priority for us is getting some heating, the old Aga that keeps only the kitchen warm has to go and we need something a bit more modern. We have filled the 50-80mm cavity with polystyrene (ThermaBead cavity Carbon Saver), which may have got the block/cavity/brick wall U value down to somewhere near 0.4. The loft has c. 200mm mineral wool. The Crittall windows will be changed at some point.

 

I'm considering a GSHP. Given our EPC's heating requirement is quite large I think the RHI could be significant, especially as we have space for trenches so don't need the expense of a bore hole (we have spring water, I've got some questions to ask on that in another post).

 

My question relates to floor insulation, or the absence of it. The ground floor is 67 sqm which is made up of 40 sqm of suspended floors (living room and dining room) and 27 sqm of concrete floors (kitchen, hall and cloak room). Taking up the suspended floor to insulate is relatively easy. Taking up the concrete floor would be a far less pleasant task. Having attempted to calculate the heating demand under a scenario where the whole floor is insulated verses one where only the suspended floor is insulated suggests it's not that big a difference. We're going to have plenty of cold bridges under the walls anyway.

 

Would it be foolish not to take up the concrete floors and do the full job? Any tips on taking up a 1950s concrete floor?

[Russell griffiths]

Big hammer 

[Nickfromwales]

Hi and welcome...back

The whole RHI scheme seems arse backwards to me but hey-ho. Be inefficient, burn more, pollute more, get rewarded......I wonder if it was a great initiative?

2 hours ago, sam said:

Would it be foolish not to take up the concrete floors and do the full job? Any tips on taking up a 1950s concrete floor?

Yup. Get the lot out. Hardcore, blind, DPM, insulation and then the new slab, and if you can get the place as draught-free as possible and the windows and doors sorted, you could even entertain underfloor heating. 

Are you doing this place up to stay there for the duration?   

[Russell griffiths]

As nick said. Your overall sq m is not that big so you could rip the lot out, hardcore, dpm,insulation,ufh, and concrete. 

[Ian]

@sam

if you do decide to replace the concrete area of floor make sure when you do the work to allow for a continuation of air flow through the area with the suspended floor. The reason suspended timber floors have air brick ventilators front and back of the house is that the moving air helps remove any risk of dry rot developing in the underfloor timbers

[A_L]

12 hours ago, sam said:

 

I'm considering a GSHP. Given our EPC's heating requirement is quite large I think the RHI could be significant, especially as we have space for trenches so don't need the expense of a bore hole (we have spring water, I've got some questions to ask on that in another post).

 

My question relates to floor insulation, or the absence of it. The ground floor is 67 sqm which is made up of 40 sqm of suspended floors (living room and dining room) and 27 sqm of concrete floors (kitchen, hall and cloak room). Taking up the suspended floor to insulate is relatively easy. Taking up the concrete floor would be a far less pleasant task. Having attempted to calculate the heating demand under a scenario where the whole floor is insulated verses one where only the suspended floor is insulated suggests it's not that big a difference. We're going to have plenty of cold bridges under the walls anyway.

 

hello and welcome,

 

In regards the GSHP as a rule of thumb you will need 50m² of land per kW of heat pump output. An alternative to insulating the whole floor is to insulate down the external walls to the top of the footings. Even without any underfloor insulation 100mm eps edge insulation to 0.67m could get you to about 0.6W/m².K

 

[sam]

Thanks for the responses.

 

@Nickfromwales

The RHI does seem a bit backwards but without it we would not consider GSHP and would put an oil boiler in, so in it's funny way I suspect it's doing what they want it to. Now we have the EPC we will improve the insulation but still the economics are only just sensible over oil.

 

We are planning to stay here so will put in sensible long term investment.

 

@Ian

Good point but actually the concrete area forms a T meaning the suspended floor forms two isolated areas as it is. The house in on a slope which may explain why the uphill side is concrete but I don't know why the hall to the front/downhill side original was concrete. 

 

Where I have measured, the underfloor area the gap is 250mm to the earth/rubble below. I'm thinking that hanging rock-wool and aluminium spread plates to keep a suspended floor would make sense. Do you think the extra expense of replacing the suspended floor area with a solid floor (obviously insulation and underfloor heating either way) would be worthwhile? A solid floor could give much more thermal "mass".

 

@A_L

We have enough space outside as we can go straight into our paddock.

 

I'm not sure I understand your suggestion. I'm still considering external wall insulation (in addition to the cavity wall insulation we have just had installed) but the quotes we have had so far have been around £30k, which really doesn't make much sense! Are you saying that just doing the bottom of the external walls would make a big difference?

[Nickfromwales]

24 minutes ago, sam said:

Are you saying that just doing the bottom of the external walls would make a big difference?

Nope. Entire elevation. 

[Nickfromwales]

I'd also look at the cost for excavation and seriously consider an ASHP. 

Youll need to run the numbers on this before jumping in. 

If either ( low grade heat ) source struggles to heat the house you'll ultimately be reinforcing with grid electric, so measure thrice, fit once ?

[sam]

On 29/01/2018 at 12:39, Nickfromwales said:

If either ( low grade heat ) source struggles to heat the house you'll ultimately be reinforcing with grid electric, so measure thrice, fit once ?

 

That's very good advice and really comes to the point why I asked the original question. The installers who I'm getting quotes from are providing heating demand calculations but I'm not sure how much I trust them. I've done my own calculations but again, I'm not really happy with these.
 

I can easily work out the energy loss where there is simple insulation but I struggle calculating the cold bridges/areas I cannot insulate. Are there rules of thumb for heat loss through internal walls which have no insulation under them or the bottom of external walls?
 

Should heating output be sufficient to (1) warm the house up from cold in a few hours, or (2) match heat loss if its on 24 hours a day or (3) something in between?

[le-cerveau]

3..

If you select (1) you are possibly over-specifying the system with the danger or overshoot and massive temperature swings unless you can control the system.

WIth (3) if the house gets cold you will never heat it up in the depths of winter.

You need more that (3), the question is how much more?  Depends oh heat loss, heating eoutput, time you are prepared to wait.....