Extension Build - some questions

B

bonnieprince

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Hi

I am in the process of getting some quotes for a utility/wc/living room extension to our house.
The finish of the roof is flat (w/ 5 degree pitch) and was wondering has anyone used pvc single ply membrane?
What is the soundproofing like etc?
Can standing seams be added to give a zinc roof effect?

Also got some quotes for aluclad windows from several Irish companies and they are all between €8500 - €10500. There is a door,wc windows and two sliding doors, one on the back of extension and one on the side.
Does this sound about right?


Thanks
bp
 
From a functional point of view, single ply membranes are perfectly fine if installed correctly. The main question I would have is where is your insulation going? Current best practice would recommend a 'warm roof' where your insulation is located in a layer above your roofing joists and just below the membrane. This will avoid having to ventilate the roofspace, which you would have to do if you lay the insulation between the rafters. Your agent should be able to advise you on this.

Regarding the zinc effect, this can look ok in certain circumstances. However, you would never build a real zinc roof at 5 degrees because it would leak, and if you did it would look 'wrong' for that very reason, so I dont think that putting the seams on your roof in order to make it look like zinc will look 'correct' for this reason.

You will probably hear a heavy downpour through your flat roof, but to be honest you will get used to this....

You dont mention if your windows are double glazed or triple glazed, but if you are getting quotes around the same price point its probably about right.
 
bonnieprince said:
Hi

I am in the process of getting some quotes for a utility/wc/living room extension to our house.
The finish of the roof is flat (w/ 5 degree pitch) and was wondering has anyone used pvc single ply membrane?
What is the soundproofing like etc?
Can standing seams be added to give a zinc roof effect?

Also got some quotes for aluclad windows from several Irish companies and they are all between €8500 - €10500. There is a door,wc windows and two sliding doors, one on the back of extension and one on the side.
Does this sound about right?


Thanks
bp
Click to expand...

You probably won't see the flat roof
I'd be tempted to put the money into a nice eaves detail and guttering and splash [sic] out for Back Inlet Gully traps all around, maybe with some uplighters or downlighters for a night time "Outer room" effect.
You could roof it with fibreglass on superply, on firrings min 50mm to give an air gap and fall, with 225mm x 50mm joists on insulated board foil backed on the underside with infill insulation between joists.

This is a Cold Roof, ventilated.
My experience each supplier of this type of roof will have their own slightly different details re specifications and build up so check it complies with their cert.
The bottom line is that it relies totall on the fibreglass outer skin to weather proof the structure.
The saving grace so that this is the material surfboards, fairings and bike helmts are made from.
Tough, and relatively easy to repair and with an obvious remedy to a possible impact crack.
Simply repair it, using glassfibre mesh and resin on a prepared and roughened up surface.

Mind you, if you're really stuck on a zinc roof, go for it, but as three-bed semi has said, watch out for the leaks.
If you keep your standing seams parallel to the fall and can do the entire roof in continuous lengths, maybe you can avoid them.
You will need to watch your fixing details and use some sort of secret securement to a substrate with a membrane backup, plus a vented space below.
Its a difficult detail to do well and I have never seen a warm zinc roof detail - trocal type membranes are the roofs I have most often seen as warm roof details.
You can have external insulation on almost any kind of roof, but exposure to weathring andmechanical damage can compromise even close cell insulation - plus you can't see the zinc!

[just don't hit a flammable membrane or insulation with a firework or throw a lit cigarette or match onto it]

If the fall runs from the main house down there will be problems with ventilating the roof, [you'll need vents either end of the vented space] but a level flashing detail at the house wall.
If the fall is parallel to the main house its easy to vent either end but you have a sloping roof, possibly a valley detail and a sloping or stepped flashing detail at the house wall.
A rendered external leaf may allow a waterproof render with bellcasting detail to be used, but leave a good high upstand to ensure the bellcasting can dry off properly.
Some geniuses take the bell down very low thinking this seals the joint, but really it just lets debris build up, saturate the bell and this spalls some frosty night.

ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.
 
Thanks for all the info guys
Some of the builders has recommended the warm roof system and i am leanng towards this. I agree about your comments about the zinc. If you cant see the feature why spend the money on it.
I like the idea of an outer room as the step off the extension is about 2ft so will be putting in some type of decking/platform.
I am being quoted at about €7000 for roofing and finishes, does this sound correct or in the right ball park?

threebedsemi The windows are double glaze.

thanks again for the excellent advice.

bp
 
I cannot comment on the price because you haven't even given the size of the building. In a recent post I have made comments on prices - seach for it and you'll find it - it was made only yesterday.

But pricing on a per square footage basis is risky with extensions.
For example factors affecting the cost include;-

  • how you access the extension
  • the work you do to open up the wall of the dwelling,
  • whether you have a downstand beam
  • whether you decide to have a flat ceiling running through
  • whether you use a proper "h" steel or rely on solids or windposts
  • whether you decide on a sliding joint andaccept some cracking or a robust mechanical connection to try toavoid the worst of it
  • whether you go deep enough on your foundations or use an engineered raft or mini-piles with beams
Even for a small extension, the structure alone can be done in many different ways.

So this is all before you get into quality of windows, doors, floor and wall finishes, fit-out, lighting, furnishing, etc.

Then there is the question of professional fees - many people dispense with professionals for small works, relying on the building who gives them the lowest price - this can turn out to be the worst pair of decisions they ever made, depending on who they employ.

Finally there is the issue of whether or not you need planning permission, and this has become a thorny issue with the passing into law of S.I. 235 of 2008 amending S.I. 600 of 2001 - again you can google both of these or read my recent posts.

ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.
 
onq said:
Then there is the question of professional fees - many people dispense with professionals for small works, relying on the building who gives them the lowest price - this can turn out to be the worst pair of decisions they ever made, depending on who they employ.
Click to expand...

Very true.

If I were to buy a second hand car for €5000, I'd certainly retain a Mechanic to have a look at it for me & give me his professional advice.
I can't see many extensions built for €5000 yet sensible people do spend vast sums of money without any professional advice.

Personally I find it very hard to understand but then as a professional I've seen lots of simple extensions turn into complete disasters.
 
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