Structural Drawings and Bill of Quantities in Kenya: Costs, Contents and Why You Need Them

Structural drawings and bill of quantities in Kenya are the two documents that turn a beautiful design into a safe, affordable building. Structural drawings tell your contractor how to make the building stand up. Meanwhile, a bill of quantities (BQ) tells you exactly what it will cost. Together, they protect your money and your family.

In this guide, we explain what structural drawings and BQs include, why counties and banks require them, and what they cost. Additionally, we cover foundations for black cotton soil, flat roofs, multi-storey buildings and rental blocks across Nairobi, Kiambu, Machakos, Kajiado, Nakuru, Mombasa and beyond.

What Are Structural Drawings?

Structural drawings are prepared by a registered structural engineer. They show how the building carries its loads safely to the ground. In other words, they describe the skeleton of your building.

They include the foundation design, columns, beams, slabs, staircases, retaining walls and roof structure. Furthermore, they specify concrete grades, steel bar sizes and spacing, and construction details. As a result, your contractor knows exactly how much steel goes where, and how thick each slab must be.

In Kenya, counties require structural drawings for approval. The engineer must be registered with the Engineers Board of Kenya (EBK). Therefore, always confirm your engineer's registration.

What Structural Drawings Include

Foundation Plan and Details

The foundation plan shows the size, depth and type of footings. For example, strip footings suit firm ground. Pad footings support columns. Meanwhile, raft foundations spread the load on weak soils.

Column and Beam Layouts

These drawings show where columns and beams go, their sizes, and their reinforcement. They are essential for maisonettes, flat roofs and multi-storey buildings.

Slab Details

Slab drawings show floor and roof slab thickness, reinforcement and openings. Flat roofs need careful slab design, especially if they will carry water tanks or a future floor.

Staircase Details

Stairs are complex structural elements. Consequently, they need their own reinforcement drawings.

Ring Beams and Lintels

Ring beams tie walls together at roof level. Lintels span over doors and windows. Both are shown with reinforcement details.

Roof Structure

For pitched roofs, the engineer designs trusses, purlins and fixings. For flat roofs, the slab design covers the roof.

Retaining Walls and Special Structures

On sloping plots, retaining walls hold back soil. Similarly, swimming pools, water towers, basements and septic tanks need structural design.

Why Structural Drawings Matter

Safety

A building without proper structural design can crack, sag or even collapse. Sadly, Kenya has seen several building collapses linked to poor design and construction. Therefore, structural drawings are not optional.

Approval

Counties will not approve plans without structural drawings signed by a registered engineer. NCA also requires them for registered projects.

Cost Control

Good structural design avoids both under-design and over-design. Under-design is dangerous. Meanwhile, over-design wastes steel and concrete. A skilled engineer finds the safe, economical balance.

Future Expansion

If you plan to add a floor later, the foundation and columns must be designed for it now. Consequently, structural drawings protect your future plans.

Foundations for Difficult Soils

Black Cotton Soil

Black cotton soil covers large parts of Machakos, Kajiado and eastern Nairobi. Areas such as Athi River, Syokimau, Mlolongo, Kitengela, Embakasi, Ruiru and Juja often have it. It swells when wet and shrinks when dry. As a result, it cracks walls and floors built on shallow foundations.

The solution is a soil test and a proper foundation design. Options include excavating to firm ground, using a raft foundation, or replacing the soil with compacted hardcore. Read more about house plans in Syokimau and Kitengela.

Sloping and Rocky Sites

Steep plots in Ngong, Kisii, Kikuyu and Murang'a need stepped foundations and retaining walls. Similarly, rocky plots may need blasting or special footings.

Coastal Sands and Coral

At the coast, sandy soils and coral rock need specific foundation designs. Moreover, salt air demands extra concrete cover over the steel. See house plans in Mombasa.

What Is a Bill of Quantities?

A bill of quantities is a detailed document that lists every material and work item in a building, with quantities and costs. It is usually prepared by a quantity surveyor.

For example, a BQ lists the cubic metres of concrete, the tonnes of steel, the number of blocks, the square metres of tiles, and the doors, windows and fittings. Each item has a rate, and the total gives the expected construction cost.

Why You Need a Bill of Quantities

Accurate Budgeting

A BQ shows the true cost before you start. As a result, you can plan your finances and avoid stalling halfway.

Comparing Contractors

When every contractor prices the same BQ, you can compare quotes line by line. Consequently, you spot inflated rates and missing items.

Bank Loans

Banks require a BQ before approving construction loans. It shows them the project's value and helps them plan drawdowns. Learn more on our financing page.

Buying Materials

A BQ tells you exactly what to buy. Therefore, you can buy in bulk, reduce waste and track deliveries.

Controlling Theft and Waste

With a BQ, you know how much cement or steel each stage needs. If more is used, you can investigate. This alone can save hundreds of thousands of shillings.

How Much Do Structural Drawings and BQs Cost in Kenya?

Costs vary with the building's size and complexity. At HousePlans Kenya, our structural drawings are priced by the engineer once the architectural drawings are final. This ensures the price reflects the real design.

For context, our architectural drawings cost:

The structural deposit is paid after the architectural drawings are cleared. County submission starts from KSh 10,000, with statutory fees separate. See our pricing page for the full process.

Structural Drawings for Different Building Types

Bungalows

A bungalow with a mabati roof has a simple structure. However, it still needs a foundation design, ring beam and lintel details. A flat roof bungalow needs a slab design too. Browse bungalow house plans.

Maisonettes

Maisonettes need column and beam frames, a suspended floor slab, stairs and often a roof slab. Therefore, structural design is critical. Browse maisonette house plans.

Apartments and Multi-Storey Buildings

Buildings of three or more floors need full structural calculations. Moreover, they often need a soil investigation and a lift shaft. Browse our 3 storey and 5 storey building plans.

Commercial and Institutional Buildings

Churches need long-span roofs. Schools need large classrooms and safe stairs. Hotels need complex frames. We design them all. See our commercial building designs.

BQ for Different House Sizes

A BQ is useful for every project size. For example, a BQ for a 3 bedroom bungalow helps a first-time builder control costs. Similarly, a BQ for a 5 storey apartment block is essential for bank financing and tendering.

As a rough guide, 2026 construction costs run about KSh 32,000 per m² for basic finishes, KSh 45,000 for standard and KSh 65,000 for premium. Use our building cost calculator for a quick estimate, then get a BQ for accuracy. Additionally, read our cost of building a house in Kenya guide.

The Soil Test: Where Structural Design Begins

A soil test, or geotechnical investigation, tells the engineer what lies beneath your plot. It measures how much load the soil can carry and whether it swells or shrinks. Consequently, the engineer can choose the right foundation type and depth.

For a simple bungalow on known firm ground, a basic trial pit may be enough. However, for maisonettes on black cotton soil, apartments and commercial buildings, a proper soil investigation is strongly recommended. The cost is small compared to the cost of a failed foundation. Furthermore, counties may ask for soil reports on larger projects.

Structural Inspections During Construction

Drawings only work if the contractor follows them. Therefore, key stages should be inspected before concrete is poured.

For example, the engineer or a trained supervisor should check the foundation excavation, the steel in footings and columns, the ring beam, and the slab reinforcement before casting. Similarly, concrete cubes can be tested to confirm strength. These checks catch missing bars, wrong spacing and weak concrete before they are hidden forever.

For larger projects, NCA requires inspections and site records. Even for a small home, however, inspections are a wise investment.

Updating the BQ During Construction

A BQ is a living document. As construction progresses, prices change and you may adjust finishes. Consequently, update the BQ regularly to track actual spending against the budget.

Many owners keep a simple spreadsheet based on the BQ. They record each purchase and payment against the BQ item. As a result, they spot overruns early and adjust before money runs out. This habit is especially valuable for diaspora clients who manage builds from abroad.

Structural Design for Extensions and Additional Floors

Adding a floor to an existing building is common in Kenya. For instance, many owners in Kasarani, Embakasi and Rongai add floors to rent out. However, this is risky without a structural assessment.

First, the engineer checks the existing foundation, columns and slab. Next, they calculate whether these can carry the new load. If not, the design may include new columns, strengthened footings or a lighter structure. Only then should construction begin. Moreover, the county must approve the extension.

Structural Drawings for Rental Blocks

Rental investors often build apartment blocks on 50×100 plots. These buildings carry heavy loads over three to six floors. Consequently, they need full structural calculations, a soil test and careful supervision. Our Umoja apartments and Kasarani apartments show typical layouts. We design the frame, slabs, stairs and water tank supports for every block.

Structural Plans Across Kenya

Ground conditions vary by region. For example, Kiambu has red soils that are generally good, while parts of Machakos and Kajiado have black cotton soil. Meanwhile, Kisii has steep slopes, and Nakuru has volcanic soils and occasional fissures. Therefore, local knowledge matters in structural design.

Steel, Concrete and Material Quality

Structural drawings specify materials, but quality depends on what arrives on site. Therefore, buy steel from reputable suppliers and check that bar sizes match the drawings. Similarly, use clean sand, well-graded ballast and fresh cement.

Concrete mix ratios matter too. For example, columns and slabs usually need a stronger mix than blinding or plain floors. Ready-mix concrete gives consistent quality on larger projects. Meanwhile, site-mixed concrete needs careful batching. Finally, curing is vital. Slabs and columns should be kept wet for at least seven days, or their strength suffers.

Structural Design for Pools, Tanks and Towers

Some elements need special structural design. For instance, a swimming pool holds tonnes of water and must not crack or leak. Likewise, an elevated water tank tower must resist wind and the weight of a full tank. Similarly, underground tanks and basements must resist soil and water pressure. We design all of these alongside the main building. See our house plans with a swimming pool for examples.

Who Prepares What: Architect, Engineer and Quantity Surveyor

Three professionals usually work together. First, the architect designs the layout and appearance. Next, the structural engineer designs the frame and foundations. Then the quantity surveyor measures everything and prices it in the BQ.

Each depends on the others. For instance, the engineer cannot design the beams until the architect fixes the room sizes. Similarly, the quantity surveyor cannot price the steel until the engineer specifies it. Therefore, working with one coordinated team avoids gaps and contradictions. We coordinate all three disciplines for our clients, so the drawings and the BQ always match.

Common Mistakes to Avoid

Letting the Fundi Decide the Steel

Many owners let fundis decide the steel and concrete. However, this leads to either dangerous under-design or wasteful over-design.

Skipping the Soil Test

On black cotton or unknown soil, a soil test is essential. It costs little compared to repairing cracked walls.

Using a BQ From Another Project

Every building is different. A BQ copied from another house will be wrong. Therefore, always use a BQ prepared for your design.

Changing the Design Without Updating Drawings

If you change the design, the structural drawings and BQ must be updated. Otherwise, they no longer match what you build.

Our Services for Structural Drawings and Bills of Quantities in Kenya

Structural Engineering Design

Our registered engineers design safe, economical structures for homes and commercial buildings across Kenya.

They work from your final architectural drawings, so everything matches.

Foundation Design for Black Cotton Soil

We design raft, pad and deep strip foundations for difficult soils in Syokimau, Athi River, Kitengela, Ruiru and beyond.

As a result, your building stays crack-free for decades.

Multi-Storey and Commercial Structures

We design frames for apartments, hotels, schools, churches and offices. This includes lifts, long spans and basements.

Bill of Quantities Preparation

We prepare detailed BQs for budgeting, tendering and bank loans. Consequently, you know your true cost before you build.

Architectural Drawings

Need the full package? We prepare architectural drawings first, with free 3D renders, interiors and MEP drawings. See our guide to architectural drawings in Kenya.

County and NCA Approvals

We submit your drawings and follow up until approval. Read our approval guide.

Bank and Financing Support

We prepare the documents banks need and connect you with partner lenders. Visit our financing page.

Build Safely and Within Budget

Structural drawings keep your building safe. A BQ keeps your budget on track. Together, they turn a risky project into a predictable one, whether you build a bungalow upcountry or an apartment block in Nairobi. Order your plans, book a site visit, or call 0725 310 112 to discuss your project.