Is it a good idea to build a 2nd floor over your existing house?

Over the years I've been asked to design about 15, second floor extensions over existing  single storey houses. On principle, I am generally in favour of recycling and reusing wherever possible, however experience has shown, that more often than not, the addition of a new floor over an existing house proves to be both uneconomical and time consuming.

Of the 15 proposals, only 4 have been built.

The owners generally draw up the plan, get a quote & decide it's more economical to sell & purchase elsewhere.

A rare case of it being economical, is the residence shown below.

A few considerations that made it economical were, 

1. Demolition would have meant a new building at about 1m above the current ground level, due to revised flood levels. (on the down side, leaving the floor at the current means that there's potential for future flooding)
2. Minimal interference with the existing roof means the ceiling and walls of the existing house would not be disturbed.
3. A complete rebuild of the carport, incorporating the new upper floor over that area, means the 2 storey component is all new construction. (once again, minimal interference to the existing structure)
4. The existing house needed new roof sheeting & gutter.

 

 The proposed residence is currently under construction, I'll post a few construction photos, while it's under way:

The example below involved major interference in order to add the new upper floor  :

Originally a 1970 Jennings home with hardwood frame and hand pitched roof (not your standard Brick Veneer home).
The extension required the removal of the roof frame and ceiling, in order to construct the new floor frame. This caused damage to the plaster cornices and electrical wiring. Adding additional bracing and tie down to some of the existing internal walls, added to the interference to the existing structure. In summary, very little of the existing structure, apart from the slab, was saved.
At the end of the project the owner / builder said it may have been better to demolish and do a new build.

The design process and challenge of creating the new home whilst working in with the existing structure is a challenge for any building designer.

It takes several years to become a competent building designer for new housing, however it takes many more to become familiar with the complexities of extending onto older buildings.

• A thorough site measure with the assistance of survey plans where they are required
• Your design brief is incorporated into the original floor plan to achieve a seamless addition to your residence 
• The most efficient and economical construction methods will be suggested
• Extensive experience in structural design of housing has given me the knowledge to anticipate construction issues before it is too late
• I also work closely with building certifier to minimise town planning issues.
• I can supply contact with builders who are very experienced with Extensions and Renovations