Advice: Roof foam insulation

We are quite far down the line in buying a small terraced house as a buy-to-let, where the cost of a new roof (in Barnsley) is estimated to cost around £3000. It currently has a 13 year old roof that appears in very good condition externally. The house is being bought for £72k.

However, the survey has revealed that a foam insulation product has been applied under the roof (supposedly with some kind of guarantee but I cannot see that it will have many years left on it). We obviously stand to lose money so far invested in solicitors, surveyors and mortgage broker fees if we pull out.

1. Should we suffer the loss and walk away?
   
   
2. If we negotiate on a reduction in purchase price, how much would it cost for the extra work involved in replacing the roof back to a conventional state (perhaps in percentage terms if you cannot give a figure)?
   
   
3. If we did purchase, would it be advisable to have the roof replaced immediately or monitor the moisture in the timbers and only replace the roof when excessive moisture dictates?
   

Thank you for your honest opinions.

Foam coatings only become a significant issue if the roof leaks persitantly. If its a recent re-roof, then it should not have any problems for may years to come, and you will see any potential probelms on your regular inspections.

As a seller, I would not entertain any reduction in the price for a roof that has nothing wrong with it. For the same reason I can't see why you would want to replace it.

You may have been reading too many scare stories.

but people don't have foam squirted onto recent roofs in good condition. They would have felt or membrane anyway.

the installers claim it will glue loose tiles into position and prevent them slipping.

Unless you can find a better house for less money, you may as well buy it.

If and when the roof needs repair or replacement (all roofs do eventually) the foam will be an inconvenience and cause additional cost. You can tuck a bit of money away each year if you want.

Yes, I have read quite a few scare stories. It was the surveyor's report though that got me researching.

It stated: .... certain repairs and/or improvements, which do not affect mortgageability, are required.
The underside of the roof covering and roof frame is concealed by sprayed foam. This type of repair can be effective but it is not yet fully proven & should be viewed as a stop gap measure pending proper stripping and re-roofing. Until this is done, the roof timbers under the insulation will be at greater risk of rot due to water penetration & reduced ventilation. The roof will have a limited life expectancy requiring regular maintenance, repair and renewal.

Surveyor is correct, especially if you have condensation in loft.

This house isn't something special, apart from its probable rotting roof. There must be 1000's of similar houses in the area, start looking.