I am currently planning an extension to the rear of my house. It’s north facing and never gets sunshine. I’ll have two external walls. The walls will have a 150 mm pumped cavity with 62.5 mm Kingspan insulated plasterboard on the inside. My U value will be about 0.15.
The sloping roof will have 150 mm Isover Metac between the rafters with 62.5 mm Kingspan inside it, also giving me 0.15 U value.
I’m planning to have a triple glazed 1800 mm X 2100 mm uPVC French door and a 2000 mm X 1100 mm uPVC triple glazed window.
On the roof I plan to have two Fakro FTT U8 Thermo windows. They have a U value of 0.58, much better than the standard Fakro and Velux windows.
Now to my dilemma……. I had hoped to install 114 cm X 118 cm roof windows with a combined area of about 2.3 m2. The roof itself will have an approximate area of 20 m2. Will these windows still lead to unnecessary heat loss, since their U value will be 4 times worse than the roof itself?
I would still have adequate light if I used their 780 cm X 98 cm windows, I reckon, but the extra light from the bigger ones would be a bonus. Help please!
The sloping roof will have 150 mm Isover Metac between the rafters with 62.5 mm Kingspan inside it, also giving me 0.15 U value.
I’m planning to have a triple glazed 1800 mm X 2100 mm uPVC French door and a 2000 mm X 1100 mm uPVC triple glazed window.
On the roof I plan to have two Fakro FTT U8 Thermo windows. They have a U value of 0.58, much better than the standard Fakro and Velux windows.
Now to my dilemma……. I had hoped to install 114 cm X 118 cm roof windows with a combined area of about 2.3 m2. The roof itself will have an approximate area of 20 m2. Will these windows still lead to unnecessary heat loss, since their U value will be 4 times worse than the roof itself?
I would still have adequate light if I used their 780 cm X 98 cm windows, I reckon, but the extra light from the bigger ones would be a bonus. Help please!
