Single-family house, Energy Saving Ordinance 2016, developer recommends additional insulation - is it sensible?

Good evening, dear community,

Our project:
Single-family house according to the new Energy Saving Ordinance 2016
Living area 150m² DIN
Roof so far 24cm mineral wool U-value 0.19
Exterior wall 17.5 Poroton + 16cm EPS U-value 0.19

Developer's proposal:

Increase roof insulation to 30cm U-value then 0.16 Additional costs 2,800,-
Increase exterior wall insulation to 20cm EPS U-value then 0.16 Additional costs 1,400,-

XPS under the floor slab is out of the question.

I would like to do without additional exterior wall insulation – I almost only have windows to the south anyway (U-value 0.6) – so there is not much wall left (max 50%)
Is the roof insulation worthwhile?

Do it or not? What do you think?

Thanks for some impressions

Michael

I would take a thicker stone and completely do without the insulation. We built monolithic with Poroton. We have a 36.5 cm wall, but the architect already said back then that according to the new energy saving ordinance he would tend to go for a 42.5 cm stone.

Proposal from the developer:

Why does he suggest that?

Why do you have a U-value of 0.19 W/m²K with 24 cm of mineral wool in the roof? Even with a lambda of 0.04 W/mK, I already get 0.16 W/m²K. What kind of roof construction is that? At least with a purlin roof, the insulation thickness is eventually limited by the rafter thickness. Whether I would glue EPS in front of Poroton... I think Manu would agree with that too.

Hi Ölschlamm,

lastdrop's question is not entirely unfounded: Why is your developer suggesting this to you? Did he miscalculate and is now afraid that with the proposed wall structure he can no longer meet the Energy Saving Ordinance 2016? And is now looking for an elegant way out?

It probably will never be cost-effective. A house size like yours will have heating costs somewhere around 500-600 € per year. And even if the additional insulation saved 25% of that (which quite certainly it won’t, but much less!!) you’re talking about 150 euros savings per year. And for that, you have to invest 4200 €. Doesn’t sound like a good idea!


sure, building monolithically is initially fancy, but usually costs a significant extra charge and you don't achieve the insulation values of an ETICS. And such a T8 Poroton block (unfilled) is also worse in soundproofing.

We therefore finally decided after some back and forth on 24 Poroton T18 plus 16 cm ETICS. That results in a U-value of 0.16, which should be sufficient.

Best regards,

Andreas

Oh, thanks for the answers

: thicker stone monolithic we also had at the beginning in the consultation. Energy Saving Ordinance would still work with 36.5 aerated concrete. With Poroton no longer, so definitely take thicker. Narrow wall with ETICS has the advantage that you waste little interior space because the external insulation comes on outside. (10x10m base plate gives 91.7m² living space with 42.5cm stone, with 17.5cm stone 96.5m² - so almost 10m² for two floors).

: He suggests that in order to still meet the Energy Saving Ordinance 2016 with a gas boiler + 10m² ST. Alternatively 6cm XPS under the base plate. Gas boiler including solar would be price-equivalent to Rotex HpSu air-water heat pump. But the additional cost of insulation is quite hefty under the aspect of amortization of additional costs with gas, because that would be added to the gas heating. XPS would “only” cost 1800, but I don’t know if I should take that risk.

: No idea kehlbalkendach, 24cm mineral why should he state a worse value than actually present?

: Your hint ultimately leads further (if the numbers are roughly correct). With an air-water heat pump I would come to about 3000 kWh p/a according to my rough calculations (annual performance factor 2.1 is realistic with panel radiators flow 45° - please no discussion, I want it this way! - and extremely drafty high altitude on the Swabian Alb about 600m above sea level - no more will be possible) so electricity for about 750 euros. With the gas system I would come to 6000 kWh minus solar thermal 1500 kWh = 4500 kWh so about 260 euros.
Savings thus roughly 500 p/a with additional costs of 9000,- (gas tank, connection, chimney sweep etc.).
Add another 100 savings through the insulation on top, so 600,- p/a. Probably still not a good idea.

Looking forward to opinions on this

michael