L_Bey
Structural
- Aug 8, 2017
- 18
We have seen a lot of townhouse construction lately, and have been having a mild disagreement in the office about how the foundations should be protected from frost. These are typical IRC townhouses, defined as
[RB] TOWNHOUSE. A single-family dwelling unit constructed in a group of three or more attached units in which each unit extends from foundation to roof and with a yard or public way on not less than two sides.
They are required to be structurally independent per IRC, but the foundations are allowed to touch:
R302.2.6 Structural independence. Each individual townhouse shall be structurally independent.
Exceptions:
1.Foundations supporting exterior walls or common walls.
2.Structural roof and wall sheathing from each unit fastened to the common wall framing.
3.Nonstructural wall and roof coverings.
4.Flashing at termination of roof covering over common wall.
5. Townhouses separated by a common wall as provided in Section R302.2.2, Item 1 or 2.
The foundation section states that footings shall be frost protected:
R403.1.4.1 Frost protection. Except where otherwise protected from frost, foundation walls, piers and other permanent supports of buildings and structures shall be protected from frost by one or more of the following methods:
1.Extended below the frost line specified in Table R301.2.(1).
2.Constructed in accordance with Section R403.3.
3.Constructed in accordance with ASCE 32.
4.Erected on solid rock.
So the question is, is the fact that there is an adjacent unit on each side sufficient to provide "otherwise protected from frost"? Or since the townhouses are required to be structurally independent does each unit need to be supported on an appropriately frost protected foundation? If in the future one unit burns down (or is not built) does the remaining structure need to be frost protected?
We already design each unit as an independent structure for shear, since that's pretty cut and dry to work by IRC townhouse requirements, but the foundation question is less clear in the code.
[RB] TOWNHOUSE. A single-family dwelling unit constructed in a group of three or more attached units in which each unit extends from foundation to roof and with a yard or public way on not less than two sides.
They are required to be structurally independent per IRC, but the foundations are allowed to touch:
R302.2.6 Structural independence. Each individual townhouse shall be structurally independent.
Exceptions:
1.Foundations supporting exterior walls or common walls.
2.Structural roof and wall sheathing from each unit fastened to the common wall framing.
3.Nonstructural wall and roof coverings.
4.Flashing at termination of roof covering over common wall.
5. Townhouses separated by a common wall as provided in Section R302.2.2, Item 1 or 2.
The foundation section states that footings shall be frost protected:
R403.1.4.1 Frost protection. Except where otherwise protected from frost, foundation walls, piers and other permanent supports of buildings and structures shall be protected from frost by one or more of the following methods:
1.Extended below the frost line specified in Table R301.2.(1).
2.Constructed in accordance with Section R403.3.
3.Constructed in accordance with ASCE 32.
4.Erected on solid rock.
So the question is, is the fact that there is an adjacent unit on each side sufficient to provide "otherwise protected from frost"? Or since the townhouses are required to be structurally independent does each unit need to be supported on an appropriately frost protected foundation? If in the future one unit burns down (or is not built) does the remaining structure need to be frost protected?
We already design each unit as an independent structure for shear, since that's pretty cut and dry to work by IRC townhouse requirements, but the foundation question is less clear in the code.
