We are in the 2nd week of our loft conversion and just had the shell of our main dormer (we are having an L Shape) go up.
The loft company we appointed covers everything from architects, roofers, plumbers, electricians etc

The architect plan which we received some months ago shows our dimensions of our main loft dormer as follows:
Width – 4940mm
Length – 4365mm

When we confirmed the measurements with the loft company they said this would be more or less guaranteed size of the room.

I have just accessed the main dormer via the hatch and had a measure up and it seems these are the actual measurements –
Width – 4500mm
Length – 3660mm

Either I have measured incorrectly or the architect has gotten this very wrong?

So far only the shell of the dormer has gone up so there is time to change things however I do not see how they will magically be able to increase the sizes since they are using the maximum width and length of the rooms.

How should I approach this matter?

Stop them building until you have confirmed what is going on.

It may delay things by half a day but will save a lot of time if they crack on and put more materials in that they then have to remove and re-do.

You sure you aren’t mixing up external and internal measurements?

In my experience working with architects, they won’t take responsibility for anything 😜

If , like you say they have built it to the maximum size they can , then it looks like the architect may have made a mistake with their measurement .

If you are taking the exact dimensions where they show them on the drawing, then I don’t see there is much you can do. Bring it up with the roofer and ask to see what drawing they are working to.

Plan for loft room –

<img src="<img src="https://thumb.ibb.co/b7nKXx/20180321_195734.jpg&quot; alt="20180321_195734" border="0" />” alt=”” />

Is it a terraced house?  Looks as wide as it can be? I think the reduction in width is because they can’t or haven’t built on the party wall but inside it.  Therefore omit the width of the walls and probably some width for flashing up to the party wall.  All that is on the assumption it’s a terraced house.

Your contract with them says that width and depth.  Perhaps you could reduce what you pay them by the reduction in cost per square metre?

It is indeed a terrace house. Agreed, the dimensions I have put down (which is the shell/wooden frame of the dormer, no insulation or plaster board as of yet) it seems cannot be any greater.