Practical and Energy Efficent House Design

[Moggaman]

Hi

Could anyone give me a view on my proposed House Design . It is rectangular in plan (mostly). Wallplate is raised to allow liveable space upstairs. The vaulted ceiling will be 225mm rafters with 225mm insulation between. The roof is all rooflights. Can anyone tell me if there is any negative aspect to installing rooflights in terms of efficency. I realise they may be a bit noisy in rain etc but is there any dangers associated with them that I should be wary of.

Thanks

[MikeGrahamT21]

I have just completed an extension in a very similar manner, vaulted ceiling with 225mm insulation (we did full fill with PIR, and then had to counter batten the roof for the 25mm air gap), and we have 2 roof windows on the south facing side which work quite well. We used Okpol roof windows, however the air tightness wasn't what we were led to believe, and I think in general airtightness in roof lights is probably an issue, so thats one thing to consider.

 

Our U Value on the roof was around 0.11 in the end, the roof windows even though they are triple glazed is 1.0U, so a lot worse, but you have the solar gain in the day time when its sunny. We have both older double glazed in another roof, and these newer triple, and the triple are a LOT quieter when it rains, you could certainly sleep with it, but you can still hear it.

 

This particular room has a lot of glazing elements, 2x2.1m bi fold doors, and a massive window at 1.6mx1.9m all triple glazed, and the room even when we have had -5c a few weeks back required around 10minutes of heating first thing in the morning and that was it for the whole day. Now with this warmer weather, the heating hasn't been on for days, holding a nice 21C. So for us, there is no negative impact in terms of efficiency.

 

One final thing to note is overheating in the summer months, this year we have decided to add on Awnings, which are external blinds that cut down heat ingress by what they say is around 80%, so we will see how they perform.