Net zero retrofit requirements

[ColdHouse]

Hi,

I own early 1990s detached house. It has cavity walls (75mm I think), which the previous owners had filled with polystyrene beads. 

The floor is uninsulated concrete. Windows are all double glazed.

I'm trying to find out what measures I going to be needing retrofit to it, the get it up to the standards needed for the UK to be net zero by 2050, but not having much joy.

 

I think the obvious ones are:

• Loft insulation,
• Replacing gas boiler with air source heat pump, 
• Fitting solar panels on the roof. 

 

But what about:

• External insulation, 
• Triple glazed windows, 
• MHVR, 
• Digging up the floor and insulating underneath? 

 

I've read about the Enerphit and AECB retrofit standards, but I can't see what they're based on or how they fit with net zero. 

In the short term I'm most interested in finding out about floor insulation. I'm wanting to replace the kitchen, so if the floor does need insulating then I'd better do that first...

 

Can anyone point me in the right direction?

 

 

[nod]

BC rely on the installers certificate 

As long as you have that they get into the technical side of things 

[jayc89]

Do you live in it? To do it properly it will need totally gutting. It will allow you to run a continuous airtight layer, route MVHR ducts appropriately etc etc. 

 

We retrofitted a concrete slab in our current house, managed to get a micro digger and dumper in through the front door to make things easier but it was a messy job.

With something like this, I'd start with a plan for AIM (Airtightness, Insulation and Mechanical Ventilation) to reduce your energy usage as much as possible, which will then help drive your APE (ASHP, PV, EV) plans to reach net zero. 

[IanR]

2 hours ago, ColdHouse said:

I've read about the Enerphit and AECB retrofit standards, but I can't see what they're based on or how they fit with net zero. 

 

While they benefit the home owner in the march towards Net Zero, there's no direct link. For homes, Net Zero will mean using an energy source that does not create CO2, for heating and hot water. For the majority of homes that will mean electricity.

 

Since the unit price of electricity is higher than that of Fossil Fuels, it's a benefit to the home owner if the energy losses are reduced as much as is practicable, so that a heat pumps will work as efficiently as possible to balance out the cost, or if you can reduce the energy losses enough then use an electrical resistive heating solution that avoids the capital investment of the heat pump. For a retrofit, is unlikely to be costs effective to go to the latter route and more likely the better solution is a heat pump, especially while there is the BUS grant to help with the capital investment.

 

To get a heat pump running efficiently, you need to reduce the flow temp, ideally in the 35°C - 40°C range. To achieve this the heat emitters (UFH / radiators) need to be sized sufficiently large to meet the heat demand at that flow temp.

 

If you can get "enough" insulation under the floor, then UFH is a very effective emitter for a heat pump powered heating system, due to the area it emits heat over. But, it's not mandatory, over-sized radiators and/or fan assisted radiators can do the job, if sized correctly.

 

With regards reducing energy losses it's all about insulation and air tightness, and spending the budget wisely. Roof, floor and walls (including windows and doors). If you have no insulation under the concrete floor, then this really does need to come up and have insulation put down under a screed. While doing this work it is cost effective to include UFH. The roof's got to be where the most cost effective gains are to be made.

 

3G windows may not be necessary. Depending on the spec of your current 2G, they may be OK, but if you do need to replace them then 3G is not such a premium.

For me, MVHR wouldn't be a focus, but air-tightness would. In England a house needs mechanical ventilation if the air-tightness is below 3m³/m².h @ 50 Pa. That's quite a high target, and not achieved by the vast majority of new builds. Adding MVHR above this level, increases the energy losses through ventilation, when it is not necessary. There are significant energy loss gains to be made by reducing the natural ventilation rate to sub 1m³/m².h @ 50 Pa, but the costs to achieve this in a retrofit will be high. It may be that targeting 3m³/m².h @ 50 Pa, including controllable trickle vents on windows and single room air extraction (possibly with heat recover) in wet rooms is the more cost effective option.

It's worth spending some time working out where it's best to spend some money, ie. an extra 25mm of insulation under the floor, or an extra 50mm in the roof. One the forum members has created a spreadsheet to help with this.

 

[akjos]

As others stated, digging up the concrete and insulating beneath is costly and messy. If you have the height, you could instead insulate above (create a floating floor).

Essentially just add rigid insulation board above your concrete slab, vapour barrier and then a liquid screed. You could even add UFH in the screed if you like. BUT you loose from the room height, so it all depends on your situation.