I have recently had a new ground floor kitchen extension completed and I have noticed two hairline cracks in the roof.
I’m a little confused; it’s a new ground floor kitchen extension but the cracks are in the roof! Do you mean ceiling?
These are pretty straight and run upwards from then bottom of the roof to the start of the velux windows. The plaster has been on for about 12 weeks now and I painted over this using water down emulsion and then a couple of normal coats.
So is it a vaulted ceiling as you would get in a loft extension? Are the cracks on the same window or on different windows? A picture may help explain things better & a guide to where/how bad they are.
Could this be just settlement and I can simply repaint over these cracks or does this sound like a cowboy plaster job? I have heard it could that the plaster board joins haven't been correctly connected.
Settlement cracks often appear in new buildings & on conventionally plastered block walls can usually be successfully repaired with filler but straight line cracks in skimmed plasterboard ceilings or dry lined stud walls are not a good sign as it usually indicates a failure along the joint line where 2 boards meet. Unfortunately, once board joint fails/cracks, it’s unlikely you’ll permanently repair it with filler & it will most likely crack again without more aggressive remedial work. As for a cowboy plastering job, there is no way of telling without seeing it, assessing how well it’s been done or if something else has caused it; what’s the finish of the plaster like? Board joint cracks are caused by movement which could be for any number of reasons;
• Movement of the new extension structure; are there other cracks?
• Insufficiently sized or badly fixed timber joists, studs or roof trusses (not sure what you have yet)
• Wet timber used in construction
• Incorrect boarding or badly located plasterboard joints (around windows etc.)
• Boards insufficiently supported particularly along joints
• Insufficient board thickness; 12.5mm are commonly used for both walls & ceilings now
• Too wide a gap left between boards (they should be close butted)
• Joints not or insufficiently tapped
• Insufficient board fixing screws
• Drying out too quickly, usually caused by central heating
• Differential expansion between two adjacent, dissimilar materials
& I’m sure there are a few others.