Shed roofs

[Chasbo]

Hi

I am using BHG Designer Pro 7 and have almost finished my 1st project with the exception of the following problem.

As the attached images show, my building block is 2-levels separated by a retaining wall. The 1st (higher) level is 2300mm above sea level and the second (lower) level is at sea level. Both levels are flat. I have used a terrain break and terrain lines to model this on BHG Pro 7.

On the 1st level there is a single storey structure with a shed roof that slopes from North to South at 8 deg (arbitrary) pitch.

On the 2nd level is a double storey structure with a shed roof that slopes from South to North at 8 deg (arbitrary) pitch.

Both structures (single and double) are supposed to butt against each other to produce a seamless single dwelling.

The problem is that I cannot get rid of the hole in the gable walls created where the two shed roof planes join. The hole can be seen on the North & South elevations of the attached images. The only way I can 'solve' it is to separate the 'butting' walls by a minimum of 210mm (this figure was found by trial and error).

The attached images are a simple test structure I created to demonstrate the problem.

Any help would be appreciated.

Many Thanks.