warping of kitchen unit backs

[tireetim]

Not sure if this is the right place to post but hoping somebody can help. I have just built some kitchen units (Homebase) with hardboard backs to the units. They aren't installed but are in my house and were for a long time before building them (no damp). I had to go away for a couple of weeks but now I've got back I have noticed that all of the hardboard backs have expanded and now bow out between the tacks that hold them to the chipboard side / top / bottom panels. It may have been a bit cold but not damp. Is this normal and what can I do to fix it (I can take the backs off and re-fix but then I guess they may shrink again and maybe damage the board). Another thought was to jut put loads of tacks in but they will still bow in the middle where they are not fixed. I'm gussing this is a common thing as most cheapish kitchens seem to be made the same way.
Any help greatly appreciated as I am about to fit them but need to fix this first.
Thanks.
Tim.

 

[JohnD]

it will be caused by damp, probably the void behind the cabs is quite cold, so the warm moist air from the room will tend to condense there.

Usually improve ventilation and reduce the sources of damp, e.g. wet washing, unvented tumble drier, possibly a plumbing leak, floor or wall with defective or absent DPC, leaky window frame, you'll have to tell us more about your kitchen to guess the cause.

//www.diynot.com/wiki/building:condensation_in_houses

 

[tireetim]

Thanks John, the units are just build and standing in my living room at the moment until the kitchen is ready for them. There doesn't seem to be any other problems with damp in that room but it would have been fairly cold as the heating was not on when I was away for 2 weeks. I'm suprised at the amount they have expanded if it was just from that. Anyway, now I'm not sure if I should take the backs off and fit them flat again or leave them as is. Seems there would always be a problem if hardboard is that sensitive?

 

[regsmyth]

I think John is right, having no heating on will increase the humidity in the room, and the hardboard will swell.
They should shrink back once the room is up to temperature....