Most cost effective way to get to passive standard using block

[Rishard]

Returning to this one, am I right in thinking xps insulation for the cavity is better than eps? The green building store said the xps held its insulating properties when in wetter environments. I’m hoping mine won’t be getting wet but it’s worth hearing other opinions.

[Rishard]

On 06/09/2023 at 23:16, Iceverge said:

 

Out of interest, here is what would happen if you took a more BREGS approach to the junction and forgot to use Aerated Concrete blocks and put in standard dense blocks everywhere. About a 100w difference in heating the house on a freezing day. 

 

 

 

 

Is this a 100w difference in heating per hour? I’m costing out insulation to fill the cavity, it’s a similar cost to concrete by volume. Obviously I don’t want to fill with concrete but I’m trying to grasp where the cost savings sit. Say I add 50mm pir to the inner face, that’s £400. Again, not going to break the bank but the question is, will it save me money in the long term? 

[Iceverge]

3 hours ago, Rishard said:

Returning to this one, am I right in thinking xps insulation for the cavity is better than eps? The green building store said the xps held its insulating properties when in wetter environments. I’m hoping mine won’t be getting wet but it’s worth hearing other opinions.

 

It depends on whether your insulation will be below the water table and will be permanently saturated. If it is I'd suggest you have greater problems. I ensured this won't happen by surrounding our house by a french drain. It may be an option for you? 

 

3 hours ago, Rishard said:

Is this a 100w difference in heating per hour?

 

Before @SteamyTea pops a gasket I'll try to get my reply in.......

 

100W refers to the power needed by the boiler to maintain the house at a certain temp on a cold day. 100w * 24hrs =2.4kWh. 

 

If you could reply with the following I could make an educated guess:

 

1.how many cold days you expect per year

2.What you expect to pay for energy 

3.how long you expect to stay in the house

4. When you plan on dying

 

I'm being facetious but at current energy prices payback is lightly to be in the 10-50 year region. 

 

If you plan on selling it ASAP and don't care about the next guys and assume energy usage won't be a factor in the house sale you'd be better off putting the money on a fancy sink and not bothering with any insulation. 

 

 

 

 

[Rishard]

Great, so it is 100w used per hour to achieve the desired temperature. It’s good to clarify. When you put it together as 2.4kWh over a 24 hour period it becomes more of a worth while saving. Apologies for my basic understanding, I’m getting there. Believe it or not I have had phpp done for my house.
 

1. He did explain a good amount with me but I wouldn’t know how to work out how many cold days a year from it…. 

 

2. current electricity 0.30 kWh

 

3. 20 years +
 

4. Not till it’s built but probably not much longer. 
 

I do care about its performance over its lifespan. This will be my family home so will have to live with the decisions… 

[Iceverge]

21 minutes ago, Rishard said:

Great, so it is 100w used per hour to achieve the desired temperature

 

Not quiet. You'd need an extra 100w running continuously (all day everyday) to maintain the extra temperature. For example of you got an old incandescent bulb and left it on or a large TV that would make up the difference. 

 

Otherwise the house would cool down. 

 

Ok ballpark payback is 15 years I'd say. 

 

24 minutes ago, Rishard said:

I do care about its performance over its lifespan. This will be my family home so will have to live with the decisions

 

Proper plan. You could use seconds PIR to make it cheaper. 

 

 

 

 

 

[SteamyTea]

Power is in watts (W, not w, and not Watt, that is the man it is named after).

A watt is a joule per second, (a joule, J, named after Joule, is the unit of energy).

To make life difficult, power is multiplied by 100 and then by time to end up with the kWh.

So energy is  now in kWh (not KWH, KwH, kw/h or anything like it).

 

The kWh is a horrible unit, especially as we have a unit for energy, the joule.

 

 

[SteamyTea]

30 minutes ago, SteamyTea said:

To make life difficult, power is multiplied by 100 and then by time to end up with the kWh.

By 1000 to make it a k (kilo, thousand)

[Iceverge]

I should clarify. It will be 100W extra heating needed only when it is cold outside. Not in summer. 

 

Cash payback is only a part of the equation but it will certainly pay someone back over the lifetime of the house, maybe even your kids or theirs.