revelation

Best Roof Surface for raised decking on a Flat Parapet Roof

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Hi All

 

We were planning to put a raised roof deck on our flat roof to run level with our walk on roof windows.  We hadn't really paid that much attention to the flat roof finish, whether it was felt, GRP or rubber.  

 

We now need to decide, what would you recommend as the best surface for a raised deck (like in the images attached)?

 It will need to support the legs that the decking boards will sit on and allow the water that drains below to easily run off.

 

 

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I used fibreglass which is virtually indestructible 

Most commercial use GRP 

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2 minutes ago, nod said:

I used fibreglass which is virtually indestructible 

Most commercial use GRP 


+1

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5 hours ago, nod said:

I used fibreglass which is virtually indestructible 

Most commercial use GRP 

 

Thank you, but do you think if its something thats done in the next few weeks will be done well considering the temperature and constant rain?

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48 minutes ago, revelation said:

 

Thank you, but do you think if its something thats done in the next few weeks will be done well considering the temperature and constant rain?

Your ok with quite low temperatures 

But both need to be bone dry 

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What would be the main advantage of fibre glass over felt?  I keep hearing different things, the guys that deal with felt rubbish GRP, the GRP guys rubbish felt.

 

 

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How will you stop those feet sinking into a felt roof in hot weather 

 

definitely GRP. 

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Felt definitely has a limited life, GRP will outlive you!, if you get a proper GRP installer they will get it right and give you a guarentee.

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Maybe a silly question, but are their different grades of fibre? What should I be looking out for or questions to ask to a installer?

 

 

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Hi all,

 

We have a bit of an issue, I have called about 5 different people to do do the GRP roof and they all all not keen to do it due to the weather.  They said they would require 3 days of good weather to do this and its unlikely that we will have that any time soon.  What would be the next best thing to use?

 

Regards

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You can get a single part product that sets with moisture in the air, it still has a mesh membrane, I intend using this on my porch, I used grp before, but not this time due to damp conditions. 

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@Russell griffithsthis sort of thing ..?

 

I’ve seen it used on porches and a small garage roof but never anything so large or structurally important as a main roof. Have they said why they need 3 days ..? Seems a lot if the roof is only 8x5 as that is the size of a large double garage. 

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1 hour ago, Russell griffiths said:

I intend using this on my porch,


It would be good if you could report back on this product.

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5 hours ago, PeterW said:

@Russell griffithsthis sort of thing ..?

 

I’ve seen it used on porches and a small garage roof but never anything so large or structurally important as a main roof. Have they said why they need 3 days ..? Seems a lot if the roof is only 8x5 as that is the size of a large double garage. 

 

Right now the membrane is down (we have ordered more insulation for the warm deck).

 

I assume its going  to take that time due to all the insulation and OSB cutting, the detailing for the gullys and around the roof windows etc and the drains its all being bonded down too.  I would have thought 2 days is enough but they have suggested 3 days to be certain.

 

 

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1 hour ago, revelation said:

I assume its going  to take that time due to all the insulation and OSB cutting, the detailing for the gullys and around the roof windows etc and the drains its all being bonded down too.  I would have thought 2 days is enough but they have suggested 3 days to be certain.


yes if insulation and all that detailing has to be done then 3 days sounds about right IMO.

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Thats the problem, the guys don't really want to do fibre because of the weather and its going to be difficult to get 3 days of good weather to ensure the right conditions for GRP.

 

So I am going to have to go for felt, or on person has recommended going for Sikalastic 650, do you have any knowledge or experience with it?

 

Regards

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6 hours ago, revelation said:

So I am going to have to go for felt, or on person has recommended going for Sikalastic 650, do you have any knowledge or experience with it?


Felt would be a last resort as it doesn’t last. EDPM should be the next choice after GRP. 
 

Has the contractor who suggested the Sika product laid it on a wood substrate before as a quick look and it seems to be used more on concrete decks, and the prep for a wood substrate seems quite detailed with carrier layers bonded to the wood etc. Would be good to see some examples where they have done it previously 

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Do more research. 

Felt would be my last choice. 

I did one evening, two hours and have found two likely products I will use. 

Have a look on you tube, Steve flat roofer, London, he does a lot of videos on failed roofs. 

I always like to look at stuff that doesn’t work. 

 

I have been on lots lots of office buildings in the past with old flat roofs done in felt and noticed how relatively light stuff has sunken into the surface over time, I have seen a 5 litre bucket sunken 6-8mm into the surface just by being up on the roof for 2-3 summers. 

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19 hours ago, PeterW said:


Felt would be a last resort as it doesn’t last. EDPM should be the next choice after GRP. 
 

Has the contractor who suggested the Sika product laid it on a wood substrate before as a quick look and it seems to be used more on concrete decks, and the prep for a wood substrate seems quite detailed with carrier layers bonded to the wood etc. Would be good to see some examples where they have done it previously 

 

Would that be general Firestone or a higher grade?

 

The contractor who suggested the Sika said he's done it before and on wood it will need a reinforcement mesh laid.  Its literally twice the cost of GRP, he said it achieves the same performance as fibre but can be laid with less worry about the weather.  Ideally I don't want to be paying twice the amount if I can have another material that will give me a suitable finish.

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18 hours ago, Russell griffiths said:

Do more research. 

Felt would be my last choice. 

I did one evening, two hours and have found two likely products I will use. 

Have a look on you tube, Steve flat roofer, London, he does a lot of videos on failed roofs. 

I always like to look at stuff that doesn’t work. 

 

I have been on lots lots of office buildings in the past with old flat roofs done in felt and noticed how relatively light stuff has sunken into the surface over time, I have seen a 5 litre bucket sunken 6-8mm into the surface just by being up on the roof for 2-3 summers. 

 

We are going to have decking on-top so if we had felt it would be shaded from the Sun/UV.  That should stop the felt from heating up significantly?

 

 

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