Greg Meyer Construction Ltd.

Retrofitting basements to existing homes.

The demand for ever increasing space in residences, and 
more restrictive planning requirements, often leaves    
basement construction as the only option available to 
increase the floor space of your home. 

Fortunately we are able to help. Retrofitting basements 
has been an accepted endeavor in North America for decades. 
The techniques are well accepted and have been proven over 
the course of time. 

The two standard types of residential construction are 
wood frame and masonry wall (brick). 
Retrofitting a basement to a wood frame home is a relatively 
simple process. The first step is to identify the location and 
orientation of the trusses and beams that make up the load 
carrying elements of the ground floor. Openings are then made 
in the existing foundation large enough to allow large steel beams 
(RSJ's) to be placed under these load carrying elements. 

Attachments between the residence and the foundation are severed 
and the structure is elevated a small distance to allow for complete 
removal of the existing foundation. Removal of the earth under the 
structure is performed and new foundation and basement walls are 
fabricated.  The structure is then lowered back onto the new basement 
walls. The foundation can then be backfilled and landscaped. 

Masonry construction presents different challenges for basement 
retrofit. Block and beam or pre-stressed concrete ground floor 
construction allows for the least complex masonry construction retrofit.    
These types of floors are strong enough to span the basement space. 

Underpinning is the most common technique used for basement wall 
construction. In simple terms, the process consists of excavating to 
expose the existing foundation and footings. The excavation is then 
deepened to the required depth and extended under the footings in 
several 1.0-1.5 meter wide pits or bays. Any substandard footing or 
foundation is removed.    

Shuttering is placed in the
newly excavated bay under
the exposed wall, and
concrete is poured in between
the shuttering.

After the concrete in
Bays #1 is strong enough to
support a load, the process
is repeated in Bays #2.

As the underpinning process nears completion, one or two adjacent 
bays are left open and shored up with steel beams. These open bays 
serve as an access portal for removal of the earth underneath the building. 
After removal of the earth in the basement space, under floor drain tile 
is laid and a concrete floor is poured. The external surface of the basement 
walls are then waterproofed with an membrane, and external foundation 
drain tile is laid. The remaining open bays are then underpinned. 
The external foundation excavation can then be backfilled and landscaped. 

Homes built on concrete slabs that rest directly on the ground add a 
different element of complexity in retrofit basements. The concrete slab 
is not sufficiently structurally sound, after removal of the earth beneath it, 
to support the loads from above. With this type of construction, 
underpinning of the slab perimeter is first performed as previously 
discussed. The concrete ground floor within the interior of the house is
then removed. Any load bearing walls are then braced and supported as 
required. The earth in the basement space is then excavated followed by 
construction of a basement floor. The ground floor is then replaced with 
either a block and beam floor or more commonly a floor of timber construction. 

As this has not been an exhaustive discussion of retrofit basements,
if you have any questions please contact us by e-mail by
clicking here. Or call us on 01323 482 832 or 07900 464 867.

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