Thank you for sending me the photo of the roof, below is a summary of the conversation we had last night.
Looking at the photo I can see that the flat roof is at the back of a property which is probably around 100 years old; I concluded this from the age of the brickwork.
The first thing that hits me when I look at this photo is the new EPDM roof with no new flashings. Close inspection shows the EPDM rubber has been laid over the old roof and looks pretty flat and sound, but the roofers have not replaced the flashings to the two parapet walls and to the drip detail into the gutter.
So you have a roof covering that will last 40 years+ but flashings that will need replacing very soon – not good! Also laying black EPDM rubber over an old, tar-based roof with no insulation is not good practice; the heat radiating down on a hot summer’s day will make the old tar roof under the felt melt and turn the roof below into a furnace. However, you have contacted me to get a cost of insulating the roof, and when you insulate the roof we can build out some of the problems if we approach this correctly.
The first thing we need to do is think about how to insulate the roof – do we turn the roof into a warm roof or a cold roof construction? I think, in this case, a warm roof construction will be the best – it’s the quickest, cheapest and easiest option, insulate over rather than inside.
So next we have to think about vapour barriers. The old felt roof would have been adequate and now it’s got the rubber over the top. We definitely know we have a continuous membrane, so realistically, unless we have a problem with weight, I can’t see why we couldn’t just lay the insulation over the old roof membranes and use them as the vapour barrier.
With regard to weight: The weight of the insulation and another layer of EPDM being laid over the old roof and the old EPDM is pretty much insig
nificant, as all the elements are lightweight. If the roof was originally designed correctly, without testing (and in practise engineers’ calculations nearly always come back with a positive result) I’m going to assume it’s the case for your roof.
So now let’s think about any other area of the roof that may need insulation to stop thermal bridging. As we are placing the insulation over the roof and not between the joists we need to close off the ends of the cavity between the joists at the gutter board end, as this is now the weak part of the insulation or the area where thermal briging will take place. This will mean the gutter board and guttering will all need removing and replacing with new after the insulation has been added. As this is a warm roof construction, no ventilation is needed to the void between the joists.
Now lets look at the flashings and how the roof meets the three other elevations. Metal flashings can be used at the two parapet wall elevations to terminate them, however this is not going to address the condition of the parapet walls. As as per our conversation I suggest that roofing materials should be dressed up the inside of the parapet walls and over to the outside edge, this way you would be encapsulating the parapet walls and giving them the same lifespan as the roofing materials used on the roof.
The last elevation is where the roof meets the tiles. The only thing we can do here is to strip back the tiles and re-lay them over the new roof and insulation to make a weather-tight joint. So unlike the other roofers who laid the first EPDM roof, we cannot conduct this work from the skylight and we will need to have scaffolding.
So now lets look at the materials options available. The main roof is flat and you like EPDM, so I suggest the main area of the roof is covered with EPDM; it’s good and cheap and lasts a long time, however it’s not the material to be using up and over the top of the parapet walls, as cutting and dressing it will take away the qualities of the materials. Joints are always going to be the first place that the roof fails, even though we are talking years down the line. So I suggest we use Triflex to cap the parapet walls; this is a reinforced liquid product and is better suited to this kind of detail.
Now it’s just down to pricing. Interestingly all of your work is upgrading for insulation so VAT will only be at 5%. You are going to send me photos so I can get quotes for the scaffolding, but assuming access is as easy as we discussed, I think the costs will be as follows:
Scaffolding: £ 700.00
Main roof area insulation and EPDM: £2,200.00
Remove old gutter boards and gutters, insulate, replace with new gutter boards and gutters (all in new UPVC): £ 700.00
Cap parapet walls with Triflex: £ 750.00
Cost for inspection by local authorities to certify the works : Approx. £ 200.00 (based on contract amounts)
Total cost: £4,550.00 + VAT at 5%
So where do we go from here? If the prices are acceptable, I need to:
- get quotations from the scaffolders
- do a proper site visit
- make sure the measurements are correct
- make sure all the above assumptions are correct
- adjust the prices to match the info gained
- make U value calculations and get them to the Local Authority to open a building notice
- organise men, materials and timing.
Firstly I need the photos of the patio and the alley from you, so I can send them to the scaffolders.