Garage Back Door slightly to Wide

[Mark 9002]

Need some advice Pls. I've ordered a UPVC door to replace an old rotten wooden door in the back of my Garage which I intend to fit myself. I consider myself to be a fairly competent DIYer ( never mind what the Missus says). The door is set in a single skin Block opening.
When I measured I measured from the Inside of the door opening as the block is exposed there. No plaster of lining of any kind ( the outside has a render screed up to the Frame. The narrowest measurement was 1000mm so ordered a door 990 mm. The door is made and on its way so no changing it now. I notice some time after ordering that for some reason the block work on the hinge side of the Door had actually been cut with a step in it. I hope the attached diagrammed explains. The door frame is fastened to the step part of the Block work so it looks like my new frame will be approx 10mm to big. I've read that uPVC door frames have ribs on the for attaching add ons. Would it be possible to cut these ribs off and reduce the door width enough to fit the opening. What other options are there ? Last route I want to go down is cutting the block work
Any advice would be appreciated

 

[ronniecabers]

You should be able to cut the ribbing off , it's not too hard to do.

 

[Mark 9002]

Thanks. I've got a cordless 165mm circular saw. I'm guessing a straight edge as a guide and fine tooth blade is best to use. Just approx how deep are the ribs usually ?

 

[ronniecabers]

They are about 5mm either side on all the profiles I've come across . Slow and steady and careful.not to cut into the main frame is the key

 

[^woody^]

Cut them with a wood saw, using the recessed flat edge of the frame as a guide.

Pack the reveal recess with some timber. You may be able to foam it, but be careful to ensure that the frame is secure and won't twist.

 

[Mark 9002]

Thanks for the great advice both. Hopefuly door will fit when ribs are off.