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How to control the cost under the cost increment of new standard assembly building

Issuing time:2020-01-06 00:00Author:Avant sports


1、 Policy analysis

On February 6, 2016, the opinions of the CPC Central Committee and the State Council on Further Strengthening the management of urban planning and Construction issued "strive to make the proportion of prefabricated buildings in new buildings reach 30% in about 10 years".

On September 30, 2016, the general office of the State Council issued the guidance of the general office of the State Council on vigorously developing prefabricated buildings (GBF [2016] No. 71). China began to promote the development of prefabricated buildings from the perspective of national strategy.

On December 7, 2017, Henan Province issued the implementation opinions of the general office of the people's Government of Henan Province on vigorously developing prefabricated buildings, and proposed the development objectives of the prefabricated buildings in Henan Province:

2、 Evaluation standard for prefabricated buildings

What is prefabricated building? How to determine the assembly rate of prefabricated buildings? How to match the most economical assembly? It is introduced to you through the evaluation standard for prefabricated buildings issued by the state in December 2017 and implemented in February 2018.

1. What is prefabricated building?

a) Prefabricated buildings shall meet the following requirements at the same time

i. The evaluation score of the main structure part shall not be less than 20 points;

II. The evaluation score of maintenance wall and internal partition wall shall not be less than 10 points;

III. full decoration;

IV. assembly rate not less than 50%

2. How to determine the assembly rate of prefabricated buildings?

a) Subject structure evaluation items: vertical components such as columns, supports, load-bearing walls, ductility wallboards, etc. the evaluation requirements shall not be less than 20 points

b) Integration of heat preservation, heat insulation and decoration, non masonry of internal partition, integration of internal partition, pipeline and decoration, with the required evaluation no less than 10 points

c) Scores of full decoration, dry construction, integrated kitchen, integrated toilet and pipeline are 3-6 points.

3、 What are the main factors that affect the cost of prefabricated buildings?

1. The relationship between construction scale and cost: the assembly type adopts factory processing, the mold cost is large, the larger the scale is, the lower the cost is. This has a high demand for our house type standardization and building standardization.

2. Structural cost increment: it is mainly reinforced concrete increment. Taking building 13 of 204 project as an example, the comprehensive unit price of cast-in-place reinforced concrete is 1360 yuan / m3 (including formwork), while the comprehensive price of prefabricated concrete components is about 4800 yuan / m3 (see the table below for details). Meanwhile, plastering can be reduced, which is equivalent to 250 yuan / m3 of concrete. The concrete content is 0.36, assuming a 50% assembly rate, the cost increase is about (4800-250-1360) * 0.36 * 50% = 574.2 yuan / m2. However, the cost of this part is related to the production scale of components. The larger the scale is, the lower the cost is.

3. Measure cost increment:

(1) Lifting cost: because the assembly type is mainly hoisting, the cost of tower crane is large. For example, the tower crane of cast-in-place structure is 18000 / month, the tower crane of assembly type is 50000, the cast-in-place structure is 7 days / floor, and the tower crane of assembly type is 5 days / floor. Taking 30 floors (480M2 / floor, 14400m2 in total) as an example, considering the influence of underground foundation, the tower crane cost increases about 10 yuan / m2;

(2) Site cost: due to the consideration of transportation, installation and other issues, the requirements for temporary roads, stacking sites and other factors on the site are large, but the increased cost of this part varies with the area of prefabricated buildings, with a large degree of dispersion.

4. Increase in design cost: due to the weak design level of the Design Institute at present, the secondary design of the prefabricated building needs to be carried out by the manufacturer, and the increase in design cost is about 15-20 yuan / m2.

5. Construction period: the construction period of the standard floor of the prefabricated building is about 5 days / floor, and the construction period of the intersection cast-in-place 7 days / floor is shortened. However, as the construction drawing needs 45 days of secondary in-depth design, and the time for the manufacturer's mold production and preparation for production needs to be considered, the advantage of shortening the time limit is not obvious.

6. High capital cost: at present, assembly manufacturers require 30% advance payment, increasing capital cost pressure.

Summary: the relationship between assembly building and production scale is large. If the assembly scale is small, the construction period advantage is also obvious, so it needs to be planned in advance. A simple calculation formula can be used for the cost calculation in the early stage: engineering cost increment = (4800-250-1380) * assembly rate * concrete content + 40.

4、 Economic planning of assembly building

1. Which building?

According to the opinions of the general office of the people's Government of Henan Province on the implementation of vigorously developing prefabricated buildings, by the end of 2020, the proportion of the whole province's prefabricated buildings in the new building area will reach 20%, the proportion of projects invested or led by the government will reach 50%, of which Zhengzhou will reach more than 30%, and the proportion of projects invested or led by the government will reach more than 60%. So which buildings are more economical?

(1) Due to the immaturity of the existing assembly technology and the long design time, try to avoid the first open area;

(2) The assembly type adopts factory processing, and the scale has a great impact on the cost. It is advisable to use the same house type building, which should be started at the standard floor;

(3) At present, the underground garage is basically in the form of large excavation. Prefabricated buildings need to consider the stacking of prefabricated components on the site, which requires a large load on the roof of the basement, considering factors such as transportation and stacking. Generally, buildings near the fire lane or near the edge of the garage should be considered.

2. How to determine the assembly technology combination?

It can be seen from the above scoring table that due to the limitation of the lowest score, the prefabricated building must be constructed by three systems: structure + enclosure + full decoration. How to combine the minimum required value of 36 points? How to choose the remaining 14 points?

(1) Main structure: combined with the calculation results of the real estate cost circle, the cast-in-place cost of beams, slabs, stairs, balconies, air-conditioning boards and other components is large due to the factors of formwork, overhanging, secondary structure, etc., and the price difference between the cast-in-place cost and the prefabricated components is small, so this part should be the main part, and the vertical components should be considered as little as possible; the overall main structure should meet the minimum score, i.e. 20 points.

(2) Enclosure

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