Publisher’s version / Version de l'éditeur:
Technical Note (National Research Council of Canada. Division of Building Research), 1954-08-01
READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.
https://nrc-publications.canada.ca/eng/copyright
Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à [email protected].
Questions? Contact the NRC Publications Archive team at
[email protected]. If you wish to email the authors directly, please see the first page of the publication for their contact information.
NRC Publications Archive
Archives des publications du CNRC
For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous.
https://doi.org/10.4224/20338395
Access and use of this website and the material on it are subject to the Terms and Conditions set forth at Concrete slabs for basementless construction
Ball, W. H.
https://publications-cnrc.canada.ca/fra/droits
L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.
NRC Publications Record / Notice d'Archives des publications de CNRC: https://nrc-publications.canada.ca/eng/view/object/?id=dbd1e7f9-14a1-4ec8-ba0e-bbc8d214b9d7 https://publications-cnrc.canada.ca/fra/voir/objet/?id=dbd1e7f9-14a1-4ec8-ba0e-bbc8d214b9d7
OF EWILplNG RESEARCK
•
DtVJSION
'fE
C
1HI N II CAlL
NOTlE
No .
181
NOT FOR PUBLICATION ,-.
,\....
ｾＬ"'--,
FOR INTERNAL USE
PREPARED BY li.H. Ball CHECKED BY
;"\.
APPROVED BY :R. F. L.
.. '
PREPARED FOR
..".
General Distribution ':August ＱＹｾＴ
...,
SUBJECT Concrete Slabs for Basementless
Construction •
po
'. •
,..'
"..
.
\-•..
r.
The purpose of this article is to discuss some of the engineering aspects of basementless house construction on floating concrete slab foundations.
Drainage:
The drainage of the building site should be carefully considered before a decision is made to construct a house on a concrete slab. In many cases this type of construction is considered because site conditions are such as to make basement construction,unsuitable either during construction or because of the possibility of having to contend with a wet basement after the house is built. Surface drainage should be away from the building site, in all directions if possible. Drainage of the excavation made in removing the top-soil should also be provided. This is required to prevent an accumulation of water in the granular base.
Some clay soils shrink on drying and swell when wet so that a cOLcrete slab on such soils ehoQld be designed to
meet such conditions without damage to the house. Unfortunately if drying does occur under a concrete slab it will almost
certainly not be uniform dry·ing. The soil under the edges of the slab may dry and shrink first so that one or all sides may lose the support of the soil. A high level of groundwater may not affect the performance of the concrete slab except where
there is likely to be considerable variation in groundwater level. Granular soils do not generally present difficulties in so far as ｴｨ･ｾ moistux'e Ｎｾｑｮｴ･ｮｴ is concerned.
Base for the Slab:
... ' ｾ Since the slab must be above surrounding ground-level to provide drainage and splash clearance, a base for the slab is necessary. Tae top-soil should be removed from the building
,.
I " . ＮＮＮｾ
2
site because of its organic nature and a base of crushed rock, gravel, or other granular material provided. A minilnum
thickness of 6 inches is recommended for the base and, whero necessary, additional thickness should be provided to raise the slab above surrounding ground-level. A granular base will help prevent the rise of moisture from the soil into the slab
by capillary action and may provide a cushion for the slab against movements in the soil beneath.
Waterproofing Between the Base and the Slab:
Water should be prevented from entering the slab from below as it may damage floor coverings. In dry well-drained locations special protection may not be necessary but, as a general rule, it is recmnmended that a moisture barrier be proviced. A layer of roll-roofing (45-pounc) is considered an adequate moisture barrier. All joints should be lapped and sealed with asphalt. Special care should be taken to prevent damage to this membrane during construction. It may be
necessary to place a thin layer of sand on the base to prevent puncturing of the memblane.
Thickness of the Slab:
The slab may be of uniform thickness, and for most locations a minimum thickness of 6 inches of concrete should be provided. For slabs of uniform thickness the base should extend beyond the slab on all sides in order to prevent the base material from being removed from under the edge of the
slab. The extended portion of the base should be covered with soil and sodded or grassed as soon as possible.
In some cases the slab thickness is increased at its edges to form l..oJhat is connnonly called a "grade-beam".
This strengthens the slab at its edges and provides a means of retaining the base in place. A grade-beam is necessary where perimeter heating ducts are included in the slab, and provides a surface against which insulation may be placed.
Reinforcement of the Slab:
Reinforcement may be necessary in the slah to ｾ･ｶＬ ｾｴ
cracking due to initial shrinkage or subsequent temperature
change. On some sites reinforcement may be essential to prevent damage to the slab due to movements in the soil under the slab as a result of frost action and variations in moisture content.
Where the house is heated by pipes or ducts placed in the slab and where the edge of the slab is well insulated-it will probably not be necessary to consider reinforcement against damage by frost action.
Protection against cracking of the slab due to shrinkage of concrete or temperature change can generally be
provided with light steel meshe Additional reinforcement of
the slab against soil movement should be designed by a competent individual and should be based on the estimated loads on the slab under various conditions.
Insulation of the Slab:
Heat loss from the floors of basementless houses is
likely to be appreciable. It should be controlled by insulation
to keep heating costs to a minimmu, to assist in maintaining
cOJufort condi t ions, and to pr'event condensa ti on on the floor
surface.
Insulation should be provided at the edges of the slab and should extend at least to the depth of the "grade-beam" if
this form of slab is used. For slabs of uniform thickness it
should extend at least six inches below the slab, or under the slab for at least two feet.
Insulation for use below ground-level should be such
that it will not absorb water. An absorbent or fibrous material
would have to be completely enclosed with a permanent waterproof
coating to be effective in use. Foamed glass, rubber, or
plastic insulations are now available and show promise for this
purposee Their structure is such that they consist of a
multitude of small, separate, "bubble-likell air-spaces which
are not cOll...'1.ected. Such m.ateriuls are lilcely to have 101-1
strength and need to be carefully protected in place with flashing or asbestos-cement board.
In the absence of performance data used in this way it is suggested that sufficient thickness of insulation be used
to provide a conductance of 0.20. Thus 1 inch of insulation
haVing a Ilk" value of 0.20 or 2 inches of insulation with a
"kll value of 0.40 should be provided.
Building Services:
Some difficulty may be experienced as a result of the
provision of sewer and water services to a house. It is
suggested that, if possible, plans be prepared so that a
minimwTI amount of disturbance to the soil under the slab will
result. Kitchen and bathrOOlTI services back-to-back near the
service side of the building would be advaltageous, both from
the viewpoint of installation and repair. Reinforcing of the
slab over service trenches should be considered.
It is suggested that the heating system for a house constructed on a concrete slab should provide means for supplying
4
hot-water panel system, a hot-water baseboard system, or a warm-air system with perimeter ducts installed in the floor.
The use of a space Qeater, the conventional hot-water convector, or radiator systems, or conventional warm-air systems ｲｾｹ not provide adequate heat to the slab to prevent freezing temperature undAr- the slab. Such conditions may
cause movement of tht slab, condensation on the floor surface near outside walls, and discomfort.
Heating pipes or ducts placed in rhe floor may require the provision of additional reinforcement or may interfere with a general reinforcement pattern.
