Foundation for a Timber Frame House in Ireland — Raft Is the Standard
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Timber frame walls are lighter than block, so a raft is usually the right foundation. Engineer specifies the slab edge detail.
Timber frame walls are lighter than block, so the foundation load is lower. A raft is usually the right foundation: €180–€260/m² of footprint. Strip is also viable on Class 1–2 ground but is less common for timber frame because the continuous insulation layer of a raft integrates better with the timber frame wall. The engineer specifies the slab edge detail — the connection between the timber frame wall and the raft. This detail is critical for airtightness (Part L 2022 requires 1–3 m³/m²·hr at 50 Pa; Passive House requires ≤0.6). A common detail is a 100 mm upstand on the slab edge, sealed to the timber frame sole plate with a continuous gasket.
TL;DR
Timber frame walls are lighter than block, so a raft is usually the right foundation. Cost: €180–€260/m² of footprint.
The engineer specifies the slab edge detail — the connection between the timber frame wall and the raft. Critical for airtightness.
Strip foundation is also viable on good ground (Class 1–2), but raft is more common for timber frame because of the continuous insulation layer.
When this matters most
You're at foundation design and the wall system is timber frame.
When this doesn't apply
You've already specified the foundation.
Frequently asked questions
What is the best foundation for a timber frame house in Ireland?
Raft is the standard: €180–€260/m² of footprint. Strip is also viable on Class 1–2 ground. Raft integrates better with the timber frame wall and provides a continuous insulation layer.
What is the slab edge detail for timber frame?
A 100 mm upstand on the slab edge, sealed to the timber frame sole plate with a continuous gasket. Critical for airtightness (Part L 2022: 1–3 m³/m²·hr; Passive House: ≤0.6).
Is a timber frame house cheaper to build than block?
Timber frame is 20–50% more expensive per m² of wall (€200–€280 vs €110–€160 for block) but faster to build and easier to hit BER A1. Net cost depends on the design and the BER target.
Sources
Building Regulations 2023, TGD-A and TGD-L. https://www.gov.ie/
Frequently asked questions
What is the best foundation for a timber frame house in Ireland?
Raft is the standard: €180–€260/m² of footprint. Strip is also viable on Class 1–2 ground. Raft integrates better with the timber frame wall and provides a continuous insulation layer.
What is the slab edge detail for timber frame?
A 100 mm upstand on the slab edge, sealed to the timber frame sole plate with a continuous gasket. Critical for airtightness (Part L 2022: 1–3 m³/m²·hr; Passive House: ≤0.6).
Is a timber frame house cheaper to build than block?
Timber frame is 20–50% more expensive per m² of wall (€200–€280 vs €110–€160 for block) but faster to build and easier to hit BER A1. Net cost depends on the design and the BER target.
When this matters most
You're at foundation design and the wall system is timber frame.
When this doesn't apply
You've already specified the foundation.
Where to go next
Branch into
Adjacent decisions at the same stage.