Energy-Efficient AAC Home

Why Private Homebuilders Choose Autoclaved Aerated Concrete: Numbers Over Words

Building your own home from autoclaved aerated concrete (AAC) is a choice increasingly made by those who think about costs not only during construction but also during operation — heating, cooling, and maintenance over the coming decades. And here is why this is not just marketing.

UDK AAC blocks are structural-thermal building products, meaning they have sufficient compressive strength to construct load-bearing walls while also offering excellent thermal insulation properties that meet current thermal resistance standards without additional insulation. UDK AAC blocks with a density of 400 kg/m³ have a thermal conductivity coefficient of λ = 0.1 W/m·°C — a figure confirmed by accredited laboratory test reports. For comparison: solid clay brick has λ = 0.67–0.81 W/m·°C — six to eight times worse. At the same wall thickness, a wall built from UDK autoclaved aerated concrete loses six to eight times less heat than a brick wall.

Choosing the Right AAC Wall Thickness: Calculations by Climate Zone in Ukraine

Ukraine is divided into two climate zones in accordance with DBN B.2.6-31:2021. The zone determines the minimum required thermal resistance of walls (R) and, accordingly, the required block thickness.

The thermal resistance of an envelope structure (R) is directly proportional to the material thickness and inversely proportional to the thermal conductivity coefficient (λ, W/m·°C).

Zone I — Colder Climate (most of Ukraine)

Normative wall R ≥ 4.0 m²·°C/W.
Covers: Kyiv, Kharkiv, Poltava, Chernihiv, Sumy, Dnipropetrovsk, Donetsk, Luhansk, Kirovohrad, Cherkasy, Vinnytsia, Zhytomyr, Khmelnytskyi, Ternopil, Rivne, Volyn, Lviv, Ivano-Frankivsk, Zakarpattia, and Chernivtsi oblasts.

Zone II — Milder Climate (southern Ukraine)

Normative wall R ≥ 3.5 m²·°C/W.
Covers: Odesa, Mykolaiv, Kherson, and Zaporizhzhia oblasts.

UDK AAC block walls 400 mm thick achieve R ≥ 3.5 m²·K/W.
Without additional external insulation, they are suitable for use in both Zone II, where normative thermal insulation requirements for walls are lower (from 3.5 m²·K/W), and Zone I, where requirements are higher (but 80% of 4.0 m²·K/W is permitted).
For the external load-bearing walls of a private home, the recommended block is 400 mm thick. It delivers R = 4.0 m²·°C/W and fully satisfies DBN normative requirements for both climate zones without any additional conditions.

Does UDK AAC Need External Insulation?

Short answer: with a 400 mm block — no.
Provided all other envelope structures meet the normative thermal resistance values under DBN, most private homes with UDK AAC block walls 400 mm wide can achieve energy efficiency class “B” or “C” — depending on the number of storeys and overall dimensions — even in the colder Zone I.
Replacing a 400 mm AAC wall with a thinner 300 mm wall plus 100 mm of additional insulation is not economically viable. Cost savings per m² of external wall only arise when using low-quality, highly combustible cheap EPS foam boards with a short effective service life. When a quality, non-combustible 100 mm insulation board is mounted on the façade, a single-layer AAC wall proves less expensive overall.
If the goal is energy class “A”, it is engineering solutions — not necessarily additional insulation — that are added to the wall system.

The second option is the most cost-effective in the long run. Investment in heat recovery ventilation and a heat pump pays back faster than an additional insulation layer — and does not require replacement after 25–30 years.

How to Achieve Energy Class "A" in an AAC Home: What Actually Makes the Difference

Walls are only part of the equation. A significant share of heat is lost through ventilation, windows, and inefficient building services. Class “A” is achieved through a comprehensive approach — here are five key factors:

1. Heat recovery ventilation — returns 70–90% of the heat from exhaust air back into the living space. One of the most effective long-term measures.
2. Heat pump instead of a gas boiler — reduces heating costs by a factor of 3–4. Particularly important given annual increases in gas and electricity tariffs.
3. Windows — at minimum a double-chamber sealed unit with a low-emissivity coating. Heat losses through windows can account for 25–30% of the overall thermal balance of the building.
4. Airtightness — air infiltration through gaps increases heating costs by 15–20%. Verified by a Blower Door test after construction is complete.
5. Building orientation — maximum glazing to the south, minimum to the north. Passive solar gain can cover up to 20% of the heating demand.

Five Common Mistakes When Building an AAC Home

1. Thick mortar joints between blocks
   Laying with cement-sand mortar at joint thicknesses of 10–15 mm creates thermal bridges that entirely negate the insulating advantages of the material. The rule: use UDK TBM thin-layer adhesive mortar at an average bed joint thickness of 2–3 mm.
2. Unprepared base for the first course
   The first course is always laid on cement-sand mortar with thorough levelling to a true horizontal plane. Any error at this stage is carried through the entire masonry.
3. Missing reinforcement in critical zones
   Zones above openings, lintels, and ring beams require reinforcement in accordance with the structural design. Neglecting this requirement creates a risk of cracking in the event of uneven foundation settlement.
4. Uninsulated floor slab edges
   Reinforced concrete floor slabs bearing on an AAC wall create a thermal bridge. The slab edge must always be insulated — otherwise significant heat loss and a risk of condensation will occur in that zone.
5. Incorrect window installation
   Windows must not be set flush with the outer face of the wall; instead, they are set back so that the frame is overlapped by the block on the street side by a minimum of 50–60 mm. This eliminates thermal bridges at the window-to-wall junction.

Need Advice on Choosing the Right Block?

UDK blocks are manufactured to DSTU standards and carry CE marking — a certificate of conformity with European standards.

View the full product range, certificates, and test reports

Calculate the required volume of AAC for your project

Frequently Asked Questions About UDK AAC Homes (FAQ)