Issue Date 31.10.2022
Main author David Grisaleña Rodríguez (VIS)
Attachment 1
BIM Execution Plan for residential deep renovation
BIM-SPEED demonstration site #1: Vitoria-Gasteiz
BIM-SPEED BIM Execution Plan Appendix 1: page 2 - 22
Contents
Table of Contents
1. PROJECT INFORMATION 4
2. INTRODUCTION 5
2.1 Purpose 5
2.2 Definitions and abbreviations 6
2.3 Norms, standards and guides 8
2.4 BIM Goals 8
2.5 The intended purpose 9
2.6 BIM uses 10
3. MANAGEMENT 13
3.1 Roles, responsibilities and authorities 13
3.2 Major project milestones 13
3.3 Survey strategy 14
3.4 Existing legacy data use 14
4. PLANNING AND DOCUMENTATION 15
4.1 Revised Project Implementation Plan 15
4.2 Mobilization 15
4.3 Trainings 15
4.4 Agreed project processes for collaboration and information modelling - communication 16
5. STANDARD METHOD AND PROCEDURE 16
5.1 Federation strategy 16
5.2 Origin and orientation 16
5.3 File naming convention 16
5.4 Agreed construction tolerances for all disciplines 16
5.5 Drawing sheet templates 17
5.6 Units 17
5.7 Level of information needed (LOIN) 17
5.7.1 Geometrical Data – (LOD) 17
5.7.2 Metadata (LOI) 18
5.7.3 Classification systems 18
5.8 Task Information Delivery Plan 18
5.9 Master Information Delivery Plan 18
5.10 Responsibility matrix 19
5.11 Acceptance criteria 19
BIM-SPEED BIM Execution Plan Appendix 1: page 3 - 22
5.12 Risk mitigation 20
5.13 Coordination Process 20
6. IT SOLUTIONS 20
6.1 CDE 20
6.2 Software versions 21
6.3 Exchange formats 22
6.4 Data safety 22
BIM-SPEED BIM Execution Plan Appendix 1: page 4 - 22
1. Project Information
Table 1 – Project information
Project Name ALDABE 26 & MANUEL DÍAZ DE ARCAYA 5: energy retrofitting and district
heating connection of two multi-storey buildings with 18 dwellings.
Asset Owner Several private owners (two multi storey private building).
Project Owner/ Client Several private owners (two multi storey private building). Visesa acts as
Delegate Promoter on behalf of the owners.
Appointing Party Visesa
Project Location and
Address
26 Aldabe Street and 5 Manuel Díaz de Arcaya Street. Coronación
District. Vitoria Gasteiz (Spain)
Contract Type / Delivery
Method
Design and renovation
Brief Project Description Renovation of two multi-storey buildings (18 dwellings) with no insulation,
poor energy performance and condensation and humidity/damp
problems. The renovation activities consisted of insulation of the building
envelope with focus on façades and roof and dwellings connection to a
new District Heating system based on biomass energy
Additional Project
Description
The buildings are at the same time demonstrator for BIM Speed and part
of Lighthouse demonstrator in SmartEnCity project funded under the
European Union’s Horizon 2020 research and innovation programme
(grant agreement No 691883). It aims to develop a systemic approach for
transforming European cities into sustainable, smart and resource-
efficient urban environments in Europe.
Design Start Date 24.01.2019
Construction Start Date 18/05/2020
Handover Date 19/05/2021
Estimated Asset Area (Net) 682,2 m2 (ALD26)
753,4 m2 (MDA5)
BIM-SPEED BIM Execution Plan Appendix 1: page 5 - 22
2. Introduction
2.1 Purpose
This BIM Execution Plan (BEP) was carried out with the aim of developing a pilot project in Vitoria Gasteiz
consisting of an energy retrofitting process to be developed over two multi-story private buildings. The
abovementioned execution plan allowed to take advantage of BIM methodology during the rehabilitation
process, reducing delivery time, cost and improving the retrofitting works result in terms of energy
efficiency.
The two demo case buildings were built in 1958. They are located in the city of Vitoria-Gasteiz, in the North
of Spain. First demonstration site is a four storeys residential building with eight flats, with a garage and a
bar on the ground floor. The second demonstration site is a 5 storeys residential building with 12 flats, with
a storage room and a bar on the ground floor. In both buildings, most of the main external walls are made
from double layer of brick an air-camera in between, cavity-wall. Others just are composed of a simple layer
of brick without any air-camera. Both buildings are not insulated and have poor energy performance with
condensation and humidity problems.
The buildings are part of Lighthouse demonstrator in SmartEnCity European Project funded under the
European Union’s Horizon 2020 research and innovation programme (grant agreement No 691883). This
project aims to develop a systemic approach for transforming European cities into sustainable, smart and
resource-efficient urban environments in Europe. The renovation activities within SmartEnCity project will
contain insulation of the building envelope with focus on façades and roof and connecting the dwellings to
a new District Heating system based on local biomass. During BIM-SPEED project new tools and solutions
supporting as-built data acquisition, designing, energy simulation and construction works have been
implemented guided by the BEP here described.
BIM-SPEED BIM Execution Plan Appendix 1: page 6 - 22
2.2 Definitions and abbreviations
Table 2 –Definitions and abbreviations
Names Abbreviations
(if applicable) Definitions
The Employer Visesa, as Delegate Promoter on behalf of dwelling owners.
The Contractor Facultative Direction implementing a comprehensive design and
execution plan of the project, according to the Contract.
The Contract The contract between the Employer and the Contractor
concluded as a result of the tender “Retrofitting works execution
in Coronación District Owner’s Community. Batch 1: Aldabe 26
and Manuela Díaz de Arcaya 5”
Building
Information
Modelling
BIM A set of technologies, processes and policies enabling multiple
stakeholders to collaboratively design, construct and operate a
facility in virtual space.
BIM Execution
Plan
BEP The "plan that explains how the Information Management aspects
of the Appointment will be carried out by the Delivery Team" ISO
19650-2 (3.1.3.1). The term Plan in BIM Execution Plan (BEP) refers
to a response to the Exchange Information Requirements and is
delivered either as online input or as a compiled Document to the
Appointing Party.
Point Cloud A set of data points in 3D created by 3D Laser Scanners to capture
an object, space or a whole building. Point Clouds can be
transformed into meshes, surfaces and even 3D objects using
specialised tools.
Documentation All documents including BIM models and other electronic
documents outlined within the BIM execution plan.
Model Element
(Element,
component)
A virtual element representing a physical or abstract object.
Calibration stage The stage in which the BEP will be configured by the Contractor
and Employer, the duration of which was outlined in the
Contract.
BIM-SPEED BIM Execution Plan Appendix 1: page 7 - 22
Global
Coordinate
System
A common coordinate system defined for all objects of the
Project embedded in ETRS89 Spanish Official Geodetic
Coordinate System.
Industry
Foundation
Classes
IFC IFC refers to a neutral/open specification (schema) and a non-
proprietary 'BIM file format' developed by buildingSMART. Major
BIM Software Tools support the import and export of IFC.
*.ifc 2x3 A digital file format for BIM Models that provides universal
approaches to collaboration in the design, construction and
operation of buildings, based on open standards and workflow
(so-called Open BIM).
BIM Model An object -based, data-rich, 3D digital model generated by a
Project Participant using a BIM Software Tool. Each discipline
will produce a BIM model according to the standards outlined
within this BIM execution plan.
Discipline Model A BIM model pertaining to a single discipline,
Native BIM Model BIM model created in a program’s native file format.
Common Data
Environment
CDE An "agreed source of Information for any given project or Asset,
for collecting, managing and disseminating each Information
Container through a managed process".
Base point of
reference
A point defined in geodetic coordinates that is the reference
point for the local coordinate systems of 3D models.
Level of
Information
LOI A description of non-graphical content of Model Components at
different project phases/stages. The Level of Information (LOI)
term is used interchangeably with Level of Information Detail.
Level of Detail LOD A description of graphical content of models at each of the
stages.
Data Drops An Information Exchange milestone, where data extracted from
the BIModel is delivered to the client/employer at predefined
intervals.
3D The 3D model contains geometric and physical parameters. A 3D
model may be mono or multi-disciplined. A 3D BIM model is a
complete multi-disciplinary model, however it may be divided
into separate files.
BIM-SPEED BIM Execution Plan Appendix 1: page 8 - 22
2.3 Norms, standards and guides
Table 3 –Norms, standards, and guides
No. Document Scope of use No of
att.
1 BIM Project Execution Planning Guide and Templates (CIC
Pennsylvania State)
BIM Uses nd
2 BS 1192:2007+A2:2016 File Codes nd
3 User’s BIM guide (Spanish Chapter from Building Smart) User guide nd
4 BIM Project Execution Guide (National esBIM comission,
2018)
BIM Uses nd
5 GuBIMclass Constructive elements
calssification system
nd
6 GDO-BIM – 2019-V01 (Bimetica Parametric Desing Service,
S.L.)
BIM objects creation
standard
nd
7 PAS 1192-6:2018
Information
management
requirements
nd
8 AEC (UK) BIM Protocol BIM Protocol nd
9 Level of Development Specification for Building Information
Models (BIMForum, http://bimforum.org/lod/).
Level of Development nd
2.4 BIM Goals
Table 4 –BIM Goals
PRIORITY
(high/med./low)
GOAL (CoS) DESCRIPTION BIM USES
High BIM model will be a useful input to support
retrofitting execution
PRE – Retrofitting As-built
modelling
High BIM model will be a useful input to improve future
maintenance tasks and to serve as witness of the
result of the actuation for dissemination purposes.
POST – Retrofitting As-built
modelling
BIM-SPEED BIM Execution Plan Appendix 1: page 9 - 22
High BIM model 3D visualization will facilitate the
execution process and communication &
dissemination tasks
3D visualization
Medium BIM model will facilitate document verification at
every stage of the project.
Coordination
Medium The BIM model should improve team coordination
at every stage of the project.
Coordination
High BIM models (PRE-retrofitting and POST-retrofitting)
will serve as demos for energy simulations.
Energy analysis
2.5 The intended purpose
Below is a more detailed description of how the BIM goals will be achieved:
1. PRE-retrofitting BIM model will be a useful input to support retrofitting execution and POST-
retrofitting BIM model will record interventions and show the exact result of the retrofitting works:
Enable effective communication between project team members.
Enable smooth coordination between Contractor and Employer/Costumer.
Enable the formation of a PRE-retrofitting model based on the point cloud of the existing
state previous to the intervention.
Enable the formation of a POST-retrofitting model based on the intervention
documentation (i.e.: drawings of executed works) after the retrofitting process.
BIM model will facilitate document verification.
2. BIM model visualization 3D will facilitate the execution process and communication &
dissemination tasks:
BIM model allows to check architectural information, elements’ location, type and material
BIM model supports correct execution and verification of carried out actuations
BIM model facilitates communication with Employer during design and execution phases
and fosters commitment between parts.
Allows effective communication and dissemination of intervention results with Employer
and within BIM Speed and SmartEnCity communities
3. The BIM model will facilitate document verification at every stage of the project while improves
team coordination.
Allows effective coordination with Employer and between partners to take decisions in
every stage of the project.
4. BIM models (PRE-retrofitting and POST-retrofitting) will serve as demos for energy simulations.
They will enable the creation of a BEM model and an energy analysis of the existing state.
BIM-SPEED BIM Execution Plan Appendix 1: page 10 - 22
They will allow testing solutions that will reduce primary energy, energy demand,
environmental impact, reduce LCC costs and global warming potential.
2.6 BIM uses
Table 5 –BIM uses
BIM Use Description Responsible
As-built modelling
PRE – Retrofitting &
POST – Retrofitting
The process of creation a BIM model of the existing state before
the building renovation and of the final state after retrofitting
intervention
The
Contractor
3D visualization The spatial presentation of the building in a realistic manner. The
Contractor
The
Employer
Coordination BIM model will facilitate document verification and team
coordination, allowing effective coordination with Employer and
between partners.
The
Contractor
The
Employer
Energy analysis The process of analyzing a building's energy performance The
Contractor
BIM-SPEED BIM Execution Plan Appendix 1: page 11 - 22
Table 6 –BIM-Speed uses
BIM-Speed Use Description Responsible
BIM-to-BEM
(Cypertherm
procedure)
Modelling and energy simulation of buildings with EnergyPlus™,
integrated in the Open BIM workflow via IFC. EnergyPlus ™ is a
calculation engine developed by the Department of Energy of
the United States of America (DOE), is one of the most used,
powerful and recognized energy simulation engines of today.
Thanks to its integration in CYPETHERM EPlus the application
becomes a powerful tool for the energy simulation of buildings,
allowing to know the energy demand, as well as the energy
performance of AC systems, energy consumption by system and
energy vector used.
The
Contractor
3DASH tool (3D Scan-
to-BIM)
The 3DASH tool automatically detects and creates BIM entities
from 3D point clouds acquired by laser scanning or
photogrammetry systems. The tool can be used by any
professional who needs to quickly model a building in BIM from
point clouds. This tool is better suited for the Collection of
existing building data phase.
The
Contractor
BIM Passport This tool offers building owners a view on what data they have
available in relation with their building.
The
Contractor
The
Employer
BIM-based Life Cycle
Cost and Asset
Management
The BIMSPEED database is composed of a number of materials
and components used for deep renovation of buildings. Building
renovation components are defined as the building elements
that can provide a contribution to the reduction of the overall
energy consumption and/or to an enhanced environmental and
economic sustainability.
The
Employer
BACN2BIM The tool allows users to collect information from sensors
(dynamic data) installed in buildings and download this data
from the BIM-Speed platform. This tool can be used by any
professional who wants to collect dynamic data from sensors
installed in buildings following the IFC standards. This tool is
better suited for the Collection of existing building data phase.
The
Employer
BIM-SPEED BIM Execution Plan Appendix 1: page 12 - 22
Multicriteria decision
making tool
The multicriteria decision-making methodology and tool assist
the selection of a suitable renovation alternative considering the
inputs of all involved in the decision-making process. In the tool,
you can establish the assessment criteria for all proposed
alternatives, collect the preferences from all involved in the
decision process regarding all criteria proposed. The result is a
ranking showing the alternatives according to their performance
in relation to the preferences collected.
The
Employer
VR/AR visualisations A methodology for creating VR models from BIM and
photogrammetric models to visualize by VR Box and Android
device or iPhone different renovation scenarios, comparing the
existing building with the variants of design solutions.
The
Employer
BIM-SPEED BIM Execution Plan Appendix 1: page 13 - 22
3. Management
3.1 Roles, responsibilities and authorities
Note: the following table is for educational purposes and shows as an example of what should be included
in a typical BIM execution plan. For the purposes of this report, the authors have decided that this
information does not need to be shared due to the public availability of this report and to protect the
personal information of participants. At the start of a project it is important to identify the roles and
responsibilities of the design teams. Table 7 is used to record the names and contact details of the
individuals fulfilling the necessary project roles.
Table 7 –Roles and responsibilities
Role
Company Name Email
Phone
Lead Designer
INDENORT PV SLU - PROVISER
IBERICA SLU
Confidential Confidential
Project Delivery Manager
INDENORT PV SLU - PROVISER
IBERICA SLU
Confidential Confidential
Construction Manager
INDENORT PV SLU - PROVISER
IBERICA SLU
Confidential Confidential
Project Information Manager
Visesa
Confidential Confidential
Task Team Manager *
Visesa
Confidential Confidential
3.2 Major project milestones
Table 8 –Major project milestones
Milestone Date
Laser Scan & Point Cloud 02.05.2019
PRE-retrofitting model 16.06.2020
Handover Date 19.05.2021
POST-retrofitting model TBD
BIM-SPEED BIM Execution Plan Appendix 1: page 14 - 22
3.3 Survey strategy
Table 9 –Survey strategy
Survey Method Delivery
Format Survey Origin Details, notes
Light detecting and
ranging (LIDAR)
.rcp (point
cloud)
.dwg
(planimetry)
Light detecting
and ranging
(LIDAR)
Scanning overlap > 30%.
Proportion of existing data in x-y-z
(balance) > 10%
Number of points added to the existing
cloud within 6mm threshold > 95%
ETRS89 georeferenced
3.4 Existing legacy data use
Table 10 –Existing legacy data use
No Description Format Author Location of the
files Comment
1 Tender documentation doc, pdf,
dwg Visesa Attachment to
tender contract N.A.
BIM-SPEED BIM Execution Plan Appendix 1: page 15 - 22
4. Planning and documentation
4.1 Revised Project Implementation Plan
The employer will present and clarify the rules outlined in this BEP for the use of the BIM-SPEED platform
and e-mail communication and will be obligatory to all project participants.
4.2 Mobilization
Table 11 –Mobilization Plan
Nº Description Status Point in BEP Comments
1 Mobilize resources
1.1 Training of project team members in the
required skills
Pending 4.3
2 Mobilize information technology
2.2 Configure and test the project’s CDE (BIM-SPEED
Platform)
Pending 6.1
4.3 Trainings
Table 12 –Trainings
Nº Description Organizer Form Participants Frequency Status
1 BIM-SPEED Platform The Employer online Project team
members,
the contractor
One-time Accomplished
BIM-SPEED BIM Execution Plan Appendix 1: page 16 - 22
4.4 Agreed project processes for collaboration and information modelling -
communication
The following table contains information on the types and frequency of BIM-related meetings.
Table 13 –Types and frequencies of BIM-related meetings
Meeting type Description Organizer Participants Frequency
Location
BIM Strategy To establish project aims and
ambitions
The
Contractor
The
Employer
The
Contractor
Monthly Online/in-
person
BIM kick-off To confirm BEP The
Contractor
The
Employer
The
Contractor
Once In person
5. Standard method and procedure
5.1 Federation strategy
For Vitoria Gasteiz demo buildings there is a unique architectural model per building with no federation
required. The size and complexity of this demo was sufficiently narrow that it was not necessary to
implement any federation strategy.
5.2 Origin and orientation
All coordinates will be based on the coordinate system ETRS89. One of the survey points will serve as the
origin and define it within the aforementioned coordinate system.
5.3 File naming convention
File naming convention should be based on the British standard BS 1192:2007+A2:2016. In any case, for this
BEP, is not necessary to fulfil with file naming convention as there will be just one single model without any
additional disciplines. The file naming process can be simplified as long as a coherent naming protocol is
chosen.
5.4 Agreed construction tolerances for all disciplines
Modelling tolerances for the construction phase of the project for each discipline should fall within the
range permitted by the current Spanish Building Technical Code (CTE 2019).
BIM-SPEED BIM Execution Plan Appendix 1: page 17 - 22
5.5 Drawing sheet templates
For the permit and construction design projects, documentation for drawings as well as tables should be
generated from 2D drawings and be in accordance with the requirements set out in the Contract.
5.6 Units
Table 14 –Project units
Units Format Accuracy
Linear* cm 2 decimal places
Surface m2 2 decimal places
Surface m3 2 decimal places
Angles ° 2 decimal places
Weight / weight kg 2 decimal places
*Site development plan units should be in [m].
5.7 Level of information needed (LOIN)
The LOIN is determined in the following tables.
5.7.1 Geometrical Data – (LOD)
The table below shows the required level of detail (LOD) required for each phase of the project.
Table 15 –LOD requirements for each project phase
Stage LOD
Description
PRE-retrofitting Model
POST-retrofitting Model
300
The Model Element is graphically represented within the Model as
a specific system, object or assembly in terms of quantity, size,
shape, location, and orientation. Non-graphic information may also
be attached to the Model Element. The project origin is defined and
the element is located accurately with respect to the project origin.
BIM-SPEED BIM Execution Plan Appendix 1: page 18 - 22
5.7.2 Metadata (LOI)
The table below shows the required level of information (LOI) required for each phase of the project.
Table 16 –LOI requirements for each project phase
Stage LOI Description
PRE-retrofitting Model
POST-retrofitting Model 200
Model may contain generalized parameters and additional
metadata regarding information related to energy figures (i.e.:
façade materials thermal performance, heat transfer coefficients)
and other parameters.
5.7.3 Classification systems
This project will make use of GuBIMClass classification system for elements.
https://www.bimcommunity.com/technical/load/140/gubimclass
5.8 Task Information Delivery Plan
See master information delivery plan.
5.9 Master Information Delivery Plan
BIM models and documentation will be delivered by the dates shown in the table below. The information
contained in the documentation should be complete and sufficient.
Table 17 –Master Information Delivery Plan
Stage
BIM Model by
discipline Project model PRE-retrofitting
Model
POST-retrofitting
Model
Architectural 09/09/2019 18/05/2020 TBD
BIM-SPEED BIM Execution Plan Appendix 1: page 19 - 22
5.10 Responsibility matrix
Each involved partner’s responsibilities are described in the table below. The following responsibilities have
been outlined: R- party responsible for task, A- authorizing/decision-making party, C- contributing party, I-
informed party.
Table 18 –Responsibility Matrix
Category
Task description
Owners
Visesa
Contractor
Organizational
BEP draft preparation I R C
BEP acceptance and coordination I R A
Submitting proposed changes to the BEP I A R
Introducing changes to the BEP I A R
Distribution of BEP findings within each organization I A R
Conducting trainings for the Employer in the scope specified in BEP I R R
CDE Platform
Delivery and configuration of the CDE platform for the transfer of BIM models
R I
Training users on the use of the CDE platform
R I
Administration of the CDE platform
R I
Uploading BIM models to the CDE platform as agreed upon in the BEP
A R
Archiving of BIM models on the servers of each own organization R R
5.11 Acceptance criteria
All project documentation and particularly BIM models should fulfil the following requirements in order to
be accepted by the Employer:
Models will be presented in IFC 2x3 format and the native format of the modelling software
used. Drawings will be presented in dwg format.
Models will contain properly defined coordinate systems (according to ETRS89) and project units
Models should not contain additional information linked to other files
Models should be produced in Spanish or English
BEM model and energy analysis will be performed for PRE-retrofitting as-built model and POST-
retrofitting as-built model
Naming convention compliance or alternative protocol as long as it is coherent
BIM-SPEED BIM Execution Plan Appendix 1: page 20 - 22
5.12 Risk mitigation
Table 19 –Possible risks and mitigation strategies
No.
Risk Impact on
project1
Probability of
occurence1
Prevention
methods
1 Lack of experience in the use of BIM models
during all project stages.
High High Training will be
conducted for
relevant parties.
Legend:
1 High/medium/low
5.13 Coordination Process
BIM models, drawings, text documents, meeting minutes, document scans, and all data drops regarding the
project should be done through BIM Speed Platform and archived.
The Contractor shall deliver all design documentation to the Employer in accordance with the Master
Information Delivery Plan. Before delivery, the Contractor shall ensure that the documentation is complete
and in accordance with the requirements set out in the BEP and the Contract. The Employer should only
have access to up-to-date BIM models provided by the Contractor and shared through BIM Speed Platform.
6. IT solutions
6.1 CDE
The model and documentation provided by the Contractor to the Employer during the process of
coordination or tasks defined by the master information delivery plan should be found in the locations
defined and administered by the Contractor through the use of the chosen CDE: BIM Speed Platform, with
access to it available at all times to the Employer. All relevant communication should occur within BIM
Speed platform as outlined in section 5.13.
All changes carried out in any file contained in BIM Speed Platform should be tracked and registered,
specifying date, person and nature of the change.
Seamless communication between users should be ensured by the Contractor, including messages or posts
related to specific files and data contained in BIM Speed Platform.
BIM-SPEED BIM Execution Plan Appendix 1: page 21 - 22
6.2 Software versions
Table 20 –Software versions to be used
Purpose Name of software Version of
software
Native format of
files Comments
Modelling Autodesk Revit 2019 .rvt
Point Cloud Autodesk ReCap .rcp
Text Files Microsoft Office 2003 and later .docx
Text Files Adobe Acrobat
Reader
.pdf
Coordination,
communication,
file repository,
CDE platform
BIM Speed
Platform
Coordination
platform and
collision detection
BIMcollab Zoom V5.2 .ifc
.bcf
BIM-SPEED BIM Execution Plan Appendix 1: page 22 - 22
6.3 Exchange formats
The following are the agreed upon formats for model and drawing file exchange:
Table 21 –Exchange file formats
Frequency
DWG DGN DWF PDF IFC 2x3 Other
Models
As
defined in
delivery
plan
X X
Drawings
Included
in each
stage
data drop
X X
Final
drawing
format
Included
in each
stage
data drop
X X X
Schedules or
spreadsheets
Included
in each
stage
data drop
X
6.4 Data safety
The Contractor ensures access to the BIM Speed platform for all parties involved. Every user will have their
own, named account created on their own. No unauthorized person will have access to the platform.
Changes may only be made through the mutual acceptance of both the Contractor and Employer.
The contractor should ensure access to the BIM Speed Platform for all involved partners. Despite of that,
for the present project, no security needs are identified beyond the basic security measures, which
guarantee that unauthorized persons will not have the access to data contained in BIM Speed Platform.
Changes may only be made through the mutual acceptance of both the Contractor and Employer.