Single storey extension - Uvalue and glazing issues

[africadan]

Im trying to work my way through building regualtions:

Im build an extention 3800x3000mm. The problem is I want to put in a large patio door (bi fold) which is 3000mmwidth.

I belive that I cant go over a ratio of 25% in windows of the internal floor area.

The internal floor area is: 9.28m2 (I also have an existing door which will be removed and belive this can be taken into the calculation - this is 2400m width = 2400x2100 = 5.04m2

Thats a total of 14.32m2 so 25% of this is only 3.58m2. This means I cant build my door how I want it!

HELP!!

Now, im told I can do a U-value calculation?? How do I do this or who do I get to do this??

Or cna I just use better quality glass - ie Pilkington K glass??

To add ot the complication I really wanted to put in a window in the roof of 1m2 and a side window of 250mm x 1500m

Any help or guidance would be grateful

Thanks

Daniel

 

[jamiedl]

If you keep a thermal break between the existing house and the extension, and you have a separate control for the heating, the 25% rule does not apply. If this is not possible there is a way you can add more insulation to another part of the extension. If this is the way you need to go let me know and ill help you calculate.

 

[africadan]

If you keep a thermal break between the existing house and the extension, and you have a separate control for the heating, the 25% rule does not apply. If this is not possible there is a way you can add more insulation to another part of the extension. If this is the way you need to go let me know and ill help you calculate.

What do you mean by a thermal break? there will be no door to the rest of the room, Im basically making one big room. Ie there is an existing kitchen of 20.4m2 and adding 9.3m2 to make one big room.

So is it back to calculations? Can i not just get better patio doors? ie pilkington K glass?

Thanks

 

[Fluffster]

You can get argon filled units which have a better u value rating and as the guys say increase the insulation in walls floors and ceilings to make up.
Pete

 

[africadan]

thanks. But how do I calculate everything? thanks in advance. dan

 

[jamiedl]

Firstly calculate the 'notional' which means using exposed floor, wall and openings. For the openings use the maximum you are allowed - 25% floor area. Multiply the area of each by the u-value they should be. This will give you the rate for each - finish by adding up all the totals. Bear in mind you can use the existing opening you covered up as an exposed opening.

Secondly calculate the 'proposed' using the openings you require (not using the opening you covered up) calculate each as mentioned in the 'notional' the difference you have between the 2 totals is what you will have to account for elsewhere.

As you can see i am terrible at explaining things - there is a worked example and explanation in the Scottish regs 2007. cheers

Ive heard you can get glass down to 1.2w/m2k but it will cost a fair bit more.

Another option would be to put a temporary set of external grade doors in, get your completion and take them out after (not that i condone this action)

 

[Robert too]

to keep it simple,

add up the area of glazing that the extension will cover up , ie old windows and doors that led to the outside air.

Now add your 25% of the proposed additional floor area , the combination of the 2 totals is the amount of glazing you can have in your extension.

If that struggles , then work out the floor area of the entire house , and assuming the existing house is double glazed , then you can have a total of 25% of the entire house area as glazing throughout the property.