pitched roof vs flat roofed extension

geoffwode

Hi there,

I'm planning on building an extension to the rear of my house (20sqm). Whilst contemporary design seems to favour the boxed, flat roof extension, I was originally going to go with a pitched roof. For some reason, I have it in my head that pitched roofs are less likely to leak and will require less maintenance in the long term. Would that be correct?

Thanks
GW

sinnerboy

It is less true today than say 25 years ago. In other words a well specified and competently installed flat roof should give 25+ years service . It is importation to note that warranties will be issued for a lesser period than this - typically 10 years. However the perception persists that flat roofs "are trouble" and sadly for the flat roof industry perception is often reality.

geoffwode

sinnerboy wrote: »

It is less true today than say 25 years ago. In other words a well specified and competently installed flat roof should give 25+ years service . It is importation to note that warranties will be issued for a lesser period than this - typically 10 years. However the perception persists that flat roofs "are trouble" and sadly for the flat roof industry perception is often reality.

Thanks for your response.

Would a 'well specified and competently installed flat roof' be more expensive than a well specified and competently installed pitched roof, for a 20sqm house extension?

Wally Runs

While you have time, try and see if the flat roof you plan will affect your home insurance! Some companies will not insure if you have more than 20/25/50% of the roof area flat. Or at least they will consider that you are a higher risk. It can take a lot of time and effort to convince them that your flat roof is a good as pitch. I speak from experience, following an extension I have more than 45% flat roof and only two will quote!

geoffwode

Wally Runs wrote: »

While you have time, try and see if the flat roof you plan will affect your home insurance! Some companies will not insure if you have more than 20/25/50% of the roof area flat. Or at least they will consider that you are a higher risk. It can take a lot of time and effort to convince them that your flat roof is a good as pitch. I speak from experience, following an extension I have more than 45% flat roof and only two will quote!

thank you. I've heard that before too.

strongback

It's an old saying but a good one in my view: "Get the water off the roof as quickly as possible"

Rainwater quickly runs off a pitched roof and into the gutters. This does not allow the rainwater as much time to find any weaknesses in the roof for water to penetrate. A tiled/slated roof has a long life and is generally maintenance free, any repairs to flashings and lead work down the road are fairly easy to do.

With a flat roof using something like Trocol (rubber membrane) or Paralon (bitumen) works well but it only takes a very small hole in the waterproofing to allow water to come through and create a leak. If the the flat roof is not constructed well with proper falls water can pond, if ponding corresponds with a very small hole in the waterproofing a problem is exasperated. It can sometimes be difficult trying to find where the water is coming through the waterproofing in these types of roofs which can be a guessing game at times.

For a small extension I would personally be more comfortable with a pitched roof as it is a form of construction small builders do well. If you want the box effect with a flat roof it is worth looking into what guarantees the builder is providing. There are not necessarily that many manufacturer approved installers for some of the flat roof systems so be careful that full guarantees are provided and the the builder/roofer is tied in to fixing any defects that might occur during the guarantee period.

cgarrad

Flat roof with glassfiber will give the best look and last forever. Pitched roofs look terrible, you will never see them on top houses.

Boats are made from glassfiber not slates ;-D

hfallada

My house has a grange with floor boards and tar. Even 90 years later its perfect. Also there are too flat roots from the 60s and both are still perfect. If it is done right it will last. Although some in insurance companies dont insure houses with more than 25% flat roofs

strongback

Most flat roof water proof membranes systems will start to have problems after 20-30 years, less if poorly installed. Some of the old asphalt roofs have lasted incredibly well it has to be said.

geoffwode

cgarrad wrote: »

Pitched roofs look terrible, you will never see them on top houses.

but you will see them on top OF houses

geoffwode

strongback wrote: »

It's an old saying but a good one in my view: "Get the water off the roof as quickly as possible"

Rainwater quickly runs off a pitched roof and into the gutters. This does not allow the rainwater as much time to find any weaknesses in the roof for water to penetrate. A tiled/slated roof has a long life and is generally maintenance free, any repairs to flashings and lead work down the road are fairly easy to do.

With a flat roof using something like Trocol (rubber membrane) or Paralon (bitumen) works well but it only takes a very small hole in the waterproofing to allow water to come through and create a leak. If the the flat roof is not constructed well with proper falls water can pond, if ponding corresponds with a very small hole in the waterproofing a problem is exasperated. It can sometimes be difficult trying to find where the water is coming through the waterproofing in these types of roofs which can be a guessing game at times.

For a small extension I would personally be more comfortable with a pitched roof as it is a form of construction small builders do well. If you want the box effect with a flat roof it is worth looking into what guarantees the builder is providing. There are not necessarily that many manufacturer approved installers for some of the flat roof systems so be careful that full guarantees are provided and the the builder/roofer is tied in to fixing any defects that might occur during the guarantee period.

Thanks for that. I'm inclined to go with pitched myself but the boxed, flat roof extension look seems to be the fashion with most architects these days, from what I can tell.

sinnerboy

An often overlooked consideration is escape from fire from first floor bedrooms. It is not that pitched roofs do not comply with fire escape regs necessarily.

But try to imagine it the awful situation of having to escape from a fire through a first floor bedroom window and with a single storey extension below you.

What type of roof would be better then?

geoffwode

Is a 'well specified and competently installed flat roof' more expensive than a pitched roof equivalent?

sydthebeat

geoffwode wrote: »

Is a 'well specified and competently installed flat roof' more expensive than a pitched roof equivalent?

no, personally i wouldnt say that... 'equivalent' would be closer to the description.

TheCitizen

Which is more expensive to construct - a flat roof or a pitched roof - does anyone know, generally.

cork2

cgarrad wrote: »

Flat roof with glassfiber will give the best look and last forever. Pitched roofs look terrible, you will never see them on top houses.

Boats are made from glassfiber not slates ;-D

I agree I have recently seen a lot of glass fibre roofs being constructed and they're brilliant. BUT under no circumstances she it be seen get a glass fibre roof with a cedar sheeted or zinc sheeted or even a plastered parapet around it. I recently saw a whole house the the design was that the glass fibre from the roof ran down and acted as a soffit and in other place it was the covering on the parapets wall. It was most sick disgusting thing I've ever seen!!!

gctest50

cgarrad wrote: »

Flat roof with glassfiber will give the best look and last forever. Pitched roofs look terrible, you will never see them on top houses.

Boats are made from glassfiber not slates ;-D

osmosis http://bit.ly/1vVSbYx


boats are made from lotsa things

cement .......

https://www.youtube.com/watch?v=IIKHRq7yjY8

https://www.youtube.com/watch?v=orHu9e6obL0