Insulating my 1970s detached bungalow

[Leedschap]

Hi All

 

Just purchased a 1970s detached dormer bungalow in north wales.  Its a full renovation project.  Heating is currently via a knackered oil fired rayburn.  Solid floors and cavity walls.   As part of the renovation works I would like to improve the insulation of the property and install a more energy efficient heating system. 

 

This is what I am currently thinking, 

 

- Walls - EPC says filled cavity, but will check this and top up if needed.  Plus - internal wall insulation on all external walls (50 mm PIR bonded plasterboard drylining using GypLyner or similar)

- Floors - 25 mm high density XPS glued to floor, engineered wood flooring on top (no battens).  Have considered relaying floor but level of disruption is off putting

- Roof - add 100 mm PIR board to dormer ceilings (there is no accessible loft as roof void is habitable space), minimum 300 mm loft insulation in eaves)

- Heating - air source heat pump.  New central heating system with oversized radiators, pipes run behind new drylining.   

- Windows and doors - replace all with A rated

 

The EPC report for the property has it down as low E rated at the moment but is not much help as the only insulation recommendations are for the solid floor!

 

This probably isn't going to be a forever house but likely will be there 10 years and we would like a nice warm property which doesn't cost a fortune to run.   Am I thinking on the right lines?

 

[Dave Jones]

25mm xps on floor isnt really going to do much. you want 300mm, while it is a couple days disruption it will enable you to have underfloor heating and mitigate the massive cold bridging into the walls.

[Marvin]

Aim to go APE 

It worth considering all the AIM and APE elements before making decisions. That is Airtightness, Insulation, Mechanical Ventilation with Heat Recovery OR Heat pump Ventilation, and Air Source Heat Pump, Photovoltaics and Electric Vehicle.

 

Some of these will not work properly without the others, and some will complement others:

 

1. A MVHR will not work properly without Airtightness.
2. An Air Source Heat Pump will have to compensate for the lack of Airtightness and/or Insulation to the degree that the benefits become questionable, especially during winter, without them.
3. An ASHP uses electricity and Photovoltaics can supply a little during winter and a lot during summer when cooling can be a problem and an ASHP can supply cooling.
4. PV can supply a little to an Electric Vehicle during winter and plenty during summer if your vehicle is at home during sunny days.
5. Extending a property and only doing AIM works to the extension will be no good, you have to do all the property within the thermal envelope. 

 

And thinking of running costs:

a)     Airtightness and Insulation should have no running costs and last (Well, loft insulation lasts over 40 years, in our experience) with the exception of UPVC  units for windows and doors, but that being said it will last 30 years?

 

b)    Our MVHR unit servicing 100m2 floor sized home uses about 260kWh a year; far far less than would be used to heat incoming cold fresh air in winter, and we clean the filters twice a year.

 

c)     ASHPs are, in my opinion, still in their infancy but we are now in the second year of use here. We were very careful to follow best practice in the design and installation of our system, did a lot of bespoke tweaking, and we now have an upgraded 1970’s timber framed bungalow that uses less than 25kWh per year per m2 of floor for heating.

 

d)    PV would be a lot less attractive if there is no ASHP or EV (or battery backup) or diverter to the hot water immersion. In my humble opinion, if you have a suitable roof you should install as much a physically possible. Electricity production costs (cost per kWh) are difficult to evaluate because it depends how much is used and how much is supplied to the grid. We decided to go with the PV cost divided by 7 years, which for us works out at £1.60ish per day. Yesterday the PV produced 12kWh all of which we used. Remember, 5kW of PV panels will not produce 5kW because you would have to have:

                         i.         No shadowing of any of the panels during sunlight hours (like trees, buildings or chimneys.

                       ii.         All the solar panels face exactly the right angle in relation to the summer solstice midday sun for their position on the planet. (Perfect angle facing south and perfect slope)

                      iii.         solar panels completely clean

                      iv.         the sun is completely unobscured

                       v.         the Inverter is 100% efficient

                      vi.         all the other losses due to cables, and equipment, and so on.

 

e)    Knowing the above PV limitations professional installers often add extra panels to make up for these losses. (Our inverter allows us to add roughly 28% more panels than its kW rating)

f)      PV panel installations will produce about one sixth of the power in the winter compared with what is produced in the height of summer.

 

g)    The electric vehicle and charging from the PV only really works if you can have the vehicle plugged in during the day and supply over 3kW from your PV (or a large proportion of that). This is why we went for the biggest PV that would fit on the roof.  We then installed a system which only charges the when the PV is on and generating over 2kW in winter and 3kW in summer. (we have a 13amp charging system).

 

So, if finances cause you to have to consider only a few in my humble opinion AIM first and go APE later. (But prepare the property for the APE works as much as you can).

 

Best of Luck

 

Marvin

[Leedschap]

On 13/02/2023 at 16:06, Dave Jones said:

25mm xps on floor isnt really going to do much. you want 300mm, while it is a couple days disruption it will enable you to have underfloor heating and mitigate the massive cold bridging into the walls.

The ceiling height is only 2.33m so looking to minimise buildup.  I had read if I understood correctly that 25mm xps would reduce heat loss by 50% so seemed worthwhile.

That said I think I am going to do some investigation on the slab construction and depth of foundations.  I can see the benefit in replacing the slab but if I have to underpin the walls it would be a non-starter due to cost I think!

[Iceverge]

It's unlightly you'll need to underpin for a 50 year old building. 

 

Your plan sounds good with a couple of points. Marvin has it nailed. 

 

1. Airtightness. Very DIYable and the most bang for your buck in terms of energy saving and comfort. Make a DIY blowerdoor fan. 

 

2. Ventilation. Needs to be mechanical, continuous  running and best of all with heat recovery. 

 

3. Floor insulation. Dig out and start again. If possible consider using the opportunity to make the already small rooms taller if possible. You'll be disrupted anyway by the dry lining.  No need for UFH means you can do it a room at a time. 

 

4. ASHP. Proceed with caution. They do not play nice with high heat loss houses. 

 

5. Windows. "A" rated unfortunately can mean little.  Good spec triple glazed UPVC with multiple compression seals won't break the bank. Make sure they are continuous with the insulation layer. 

Again you can do one room at a time if needed. 

 

Good luck!

 

 

 

 

 

 

 

 

[Dave Jones]

14 hours ago, Leedschap said:

The ceiling height is only 2.33m so looking to minimise buildup.  I had read if I understood correctly that 25mm xps would reduce heat loss by 50% so seemed worthwhile.

That said I think I am going to do some investigation on the slab construction and depth of foundations.  I can see the benefit in replacing the slab but if I have to underpin the walls it would be a non-starter due to cost I think!

 

buildup doesnt matter you are digging down.

 

25mm isnt going to do much, 50% (even believing that figure) loss means you need double the heat output. Madness.

 

 

[Iceverge]

On 13/02/2023 at 10:55, Leedschap said:

Just purchased a 1970s detached dormer bungalow in north wales. 

 

I would live in the house for a year. Mend the Rayburn boiler. And track the energy usage. 

 

You never know. After a year it might not be as cold as you think or you may want to knock it to the ground. 

[Leedschap]

7 hours ago, Dave Jones said:

 

buildup doesnt matter you are digging down.

 

25mm isnt going to do much, 50% (even believing that figure) loss means you need double the heat output. Madness.

 

 

I’m coming round to the idea of digging it out.  Of course, if I’m doing that I will put in a decent amount of insulation.  I may also be able to eek out another 10cm of head room which would be a bonus.

 

I think the thing that confuses me is is the EPC lists solid floor insulation as the first thing to do, but it only raises the score by 1!! From 43 to 44.  Which implies it is of limited value but of course I know this is not the case.

 

 

[Dave Jones]

13 hours ago, Leedschap said:

I’m coming round to the idea of digging it out.  Of course, if I’m doing that I will put in a decent amount of insulation.  I may also be able to eek out another 10cm of head room which would be a bonus.

 

I think the thing that confuses me is is the EPC lists solid floor insulation as the first thing to do, but it only raises the score by 1!! From 43 to 44.  Which implies it is of limited value but of course I know this is not the case.

 

 

 

dont take too much notice of EPC its junk science at least at the moment where electric is penalised.

 

Hire in a micro digger and tracked dumper (both go through a front door) for a weekend and you'll have it done. 300mm of XPS insulation would be great. 150/200mm hardcore+sand blinding+ 150/200 conc then screed on top. Just work down from FFL to see your max depth, careful not to smash any drains.

 

 

100mm pipe spacing allows underfloor flow temp to run lower and much more efficiency for the small extra cost of a bit more pipe. Dont bother with zoning the underfloor it just reduces efficiency.

[Sophiae]

On 17/02/2023 at 09:03, Dave Jones said:

 

dont take too much notice of EPC its junk science at least at the moment where electric is penalised.

 

Hire in a micro digger and tracked dumper (both go through a front door) for a weekend and you'll have it done. 300mm of XPS insulation would be great. 150/200mm hardcore+sand blinding+ 150/200 conc then screed on top. Just work down from FFL to see your max depth, careful not to smash any drains.

 

 

100mm pipe spacing allows underfloor flow temp to run lower and much more efficiency for the small extra cost of a bit more pipe. Dont bother with zoning the underfloor it just reduces efficiency.

I am likely to follow your advice on this, however I would like to have UFH throughout the property, I can’t have radiators for child safety reasons. 
Do I have to dig all rooms together? I mean I won’t be living there but was thinking of the work load but the space/time. Would it all be possible to dig all with existing partition walls in place? 
 

[Dave Jones]

it depends if the internal walls are structural (holding up the roof), they could just be built off the pad.

 

The more internal walls you can remove the easier and better the insulation will be, walls can be rapidly built in stud after. 

[billt]

14 hours ago, Sophiae said:

 I can’t have radiators for child safety reasons.

 

?

What safety reasons are they? If you are talking about radiator temperatures it is perfectly possible to design a system with radiator temperatures at 43C or below, the maximum temperature recommended for radiators in properties with vulnerable people.

 

You may want UFH for other reasons but child safety isn't a compelling one.

 

(An online search reveals an industry devoted to exploiting fears of dangerous radiators, so I assume that there's been some sort of social media panic about them.)

[TonyT]

15 hours ago, Sophiae said:

I am likely to follow your advice on this, however I would like to have UFH throughout the property, I can’t have radiators for child safety reasons. 
Do I have to dig all rooms together? I mean I won’t be living there but was thinking of the work load but the space/time. Would it all be possible to dig all with existing partition walls in place? 
 

 

better to get it all done at once, the vibrations, noise, dust, cost for removal of material and hire of equipment, why pay multiple times?

[TheMitchells]

Any update on this?? What did you end up doing?