Extension roof choice

NDB

We've an end of terrace house and we're looking to get a 30m2 extension. It'll go out to the side and around the back. All along I've had in my head that we'd have a pitched roof on it, but we got the architects plans today and he's put a flat roof on there. If we go with pitched then we'll have to resize one of the upstairs windows.

What are the cost differences between pitched and flat? Is resizing a window much of a job? All windows in the house will be getting replaced anyway at the same time the extension is done.

goz83

I went with a flat roof for a 25sqm kitchen extension and I am glad I did. It was easier, cheaper and imo, looks better. It’s also less intrusive . I went a fibreglass roof too.

NDB

I'm looking at fibreglass now, was it much cheaper?

goz83

NDB wrote: »

I'm looking at fibreglass now, was it much cheaper?

A fair bit cheaper. I ordered a kit from up north and we did the roof ourselves with no previous experience. The kit costs around €500 for 30SQM. I went for the thicker matt which is designed for walking on. Unfortunately, the standard kit has a thinner matt, so if you want a thicker one, you have to go through the shop and pick each item one by one.

You also need to look at the trims and flashing, which you can also get in pre-formed fibreglass moulds. That will add another €100ish to the cost.

Of course the roof needs to be boarded, just like any flat roof. So you need to add about €250 for OSB3 boards. You will need about 10 boards plus misc. I recommend T&G (tongue and groove) if you can get them, but the regular boards work fine.

So €1k should cover materials cost and with 2 or 3 people going at it, the job will be done inside of a day. Perfect time of year for fibre-glassing too.

There are a couple of companies who will do it professionally, but I wanted to do it myself and I am glad I did. Saved a few quid too.

Bracken81

Flat roofs are the business these days, even though they still seem to have a bad reputation, due to not being constructed properly years ago

Fibreglass and Trocal are 2 of the best finishes for a Flat roof
Although Zinc does look great, but quite expensive

ted1

Bracken81 wrote: »

Flat roofs are the business these days, even though they still seem to have a bad reputation, due to not being constructed properly years ago

Fibreglass and Trocal are 2 of the best finishes for a Flat roof
Although Zinc does look great, but quite expensive

A well earned reputation, ever body I know who has a fibreglass roof had developed leaks

goz83

ted1 wrote: »

A well earned reputation, ever body I know who has a fibreglass roof had developed leaks

I just don't believe that, unless the same cowboy did all of them and did a crap job.

I did a huge amount of research into fibreglass roofs before deciding on one and the key thing (imo) is to over do it and do it properly. I must have watched over 30 hours of installation videos and read pages and pages of what to do and what not to do. I used to "aswell as", rather than the "instead of" approach.

I came across articles and blogs about leaking fibreglass roofs. In almost every single case, there were no lashings or mouldings used. It's vital to use moulded trims and flashing, as there will be inevitable movement at the seams and the moulding allow that bit of movement without causing de-lamination.

So, I used fibreglass trims and flashings around the parapet wall and the mating section. I used wooden fillets for the window surrounds and glassed over those, making a neater and rounder join/seal. I also used CSM twice as thick as I needed, so I can walk on the roof without risking damaging it. Not to mention I used twice the amount of resin I needed and applied two top coats. It's solid.

The roof is up less than a year, so time will tell how good it is. I reckon it's a great job in contrast to my friends mums pitched and tiled roof which had massive leaks after a few weeks which needed to be stripped and redone last year costing a few quid.